Merge origin/main (license, compose, #65 leak guard) into cans work

2026-09-09 16:39:14 -05:00
parent 5b9be808ed ffc10c2b86
commit cd70dd0b0e
22 changed files with 2293 additions and 18 deletions
@@ -0,0 +1,679 @@
 Palette - self-hosted pastebin with paste cans
 Copyright (C) 2026 poslop
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 of the code.  There are many ways you could offer source, and different
 solutions will be better for different programs; see section 13 for the
 specific requirements.
  You should also get your employer (if you work as a programmer) or school,
 if any, to sign a "copyright disclaimer" for the program, if necessary.
 For more information on this, and how to apply and follow the GNU AGPL, see
 <https://www.gnu.org/licenses/>.
@@ -77,10 +77,41 @@ curl -X POST http://localhost:8080/api/pastes \
  -d '{"content": "print(hello)", "language": "python", "expires_in": "168h"}'
 ```
-Full API docs: [docs/API.md](docs/API.md).
+Full API docs: [docs/API.md](docs/API.md). Design docs: [docs/design/](docs/design/) (currently: [client-side E2E encryption](docs/design/e2e-encryption.md), issue #39).
 ## Performance Notes
 The history and Saved pages use client-side filtering: when you type in the
 search box, the UI fetches the most recent 100 pastes (`limit=100`, the API
 maximum) once per query and filters/sorts them in the browser. Pastes beyond
 the newest 100 are not searched; a match count against the full total is still
 shown. This keeps search instant without a server-side query. If large
 instances need full search later, it will be a server-side endpoint (see
 issue #32).
 ## CI
 Gitea Actions workflow at `.gitea/workflows/ci.yml`:
 - On push to main: `go vet` + `go test`
 - On tags: build and push Docker image to `git.archfox.org/poslop/palette`
 ## Docker Compose
 See [docker-compose.yml](docker-compose.yml) for a ready-to-use example with
 every environment variable documented, including which are required (only the
 /data volume) and which are optional.
 ## License
 Palette is licensed under the GNU Affero General Public License v3.0
 (AGPL-3.0-only). See [LICENSE](LICENSE).
 The software is provided AS IS, without warranty of any kind, express or
 implied, including merchantability and fitness for a particular purpose.
 In no event shall the authors be liable for any claim, damages, or other
 liability, including without limitation any security vulnerabilities,
 data loss, or legal issues arising from use of the software. You use it
 at your own risk.
 If you run a modified version of Palette as a network service, the AGPL
 requires you to offer your modified source code to its users.
@@ -0,0 +1,46 @@
 # Example docker-compose deployment for Palette.
 # All environment variables are optional; sensible defaults apply.
 # The only hard requirement is a volume on /data so the SQLite database
 # and the auto-generated admin key survive restarts.
 services:
  palette:
    image: git.archfox.org/poslop/palette:v0.2.2
    # image: git.archfox.org/poslop/palette:latest   # tracks main, less stable
    restart: unless-stopped
    ports:
      - "8080:8080"          # host:container; the app listens on :8080
    volumes:
      - palette-data:/data   # REQUIRED: SQLite db, admin key, attachments
    environment:
      # Address the server binds to inside the container.
      # Default: ":8080". Only change if you also change the ports mapping.
      PALETTE_ADDR: ":8080"
      # Path to the SQLite database file.
      # Default: "/data/palette.db". Keep it on the /data volume.
      PALETTE_DB: "/data/palette.db"
      # Admin API key for /admin/api/settings (rate limits, size caps, expiry).
      # Default: random key generated on first start and persisted to
      # /data/admin-key (mode 0600). Read it with:
      #   docker compose exec palette cat /data/admin-key
      # Set this only if you want a fixed key (e.g. for automation).
      # PALETTE_ADMIN_KEY: "change-me"
      # Max size in bytes of a single text paste. Oversized creates get 413.
      # Default: 5242880 (5 MiB).
      # PALETTE_MAX_TEXT: "5242880"
      # Max size in bytes of a single can item (file/text inside a can).
      # Default: 26214400 (25 MiB).
      # PALETTE_MAX_ITEM: "26214400"
      # HMAC secret for password-unlock cookies. Default: random per start,
      # which logs out every unlocked browser session on restart. Set a fixed
      # secret (any random string) to keep unlock sessions across restarts,
      # or when running multiple replicas that must agree.
      # PALETTE_UNLOCK_SECRET: "generate-with-openssl-rand-base64-32"
 volumes:
  palette-data:
@@ -22,6 +22,10 @@ curl -X POST http://localhost:8080/api/pastes \
 - `expires_in` is a Go duration string (`90m`, `6h`, `336h`). Omit for no expiry.
 - `visibility` is `public` or `unlisted`.
 - Alternatively (or additionally), `public` may be sent as a boolean (#83):
  `false` maps to `unlisted` and `true` maps to `public`. When both fields are
  present, the boolean `public` takes precedence over the string `visibility`.
  Omitting both defaults to `public`.
 - `burn_after_reads` sets how many reads the paste survives (default 1 when
  `burn_after_read` is true). A read is counted per unique viewer session;
  the same viewer returning within 15 minutes does not count again.
@@ -0,0 +1,78 @@
 # Attachments & Storage Backend Design (#38, #31)
 Status: research/design, no implementation. Consumers: paste cans (#4).
 ## Part A — Attachments: S3/MinIO vs filesystem-on-volume (#38)
 ### Options
 **Option 1: Filesystem on the k3s PVC (current 5Gi volume).**
 Store blobs under `<data-dir>/attachments/<paste-id>/<n>-<sha256-8>`, metadata in SQLite (paste_id, filename, size, sha256, mime, created_at).
 - Pros: zero new infra, zero new credentials, trivial backup (the volume backup job already covers the DB), atomic rename on write, works in dev and prod identically.
 - Cons: volume is size-capped (5Gi today; resizable but bounded); serving large files passes through the app process (no ranged-GET offload); multi-replica later would need RWX volume.
 **Option 2: MinIO via S3 API.**
 MinIO is already proven in this homelab (Outline). Store at key `<paste-id>/<n>`; same SQLite metadata row.
 - Pros: effectively unbounded capacity, presigned URLs (direct browser download, offloads serving from palette pods), ranged requests free, lifecycle rules could auto-expire orphaned objects.
 - Cons: another credential/secret to manage, another failure mode, MultipartForm still terminates at the palette pod (MinIO only helps *serving*, not *uploading*, unless we do presigned uploads — which breaks the cans multipart flow and the auth/unlock checks), backup now spans two systems.
 ### Key considerations
 - **Upload path is the same either way.** Palette receives `multipart/form-data` (cans need text items + file drops in one request), must enforce auth/password/burn rules server-side. A filesystem backend adds no upload complexity; S3 adds an extra hop (buffer → PUT to MinIO). Streaming straight from `multipart.Reader` to the sink works for both (`io.Copy` to a temp file, or to an S3 PUT with `Content-Length` known or multipart buffering).
 - **Size limits.** Everything is admin-tunable via the settings API (#40 pattern) — add `max_attachment_bytes` (default 10 MiB, hard server-side cap checked *before* reading the body via `Content-Length`, plus a counted reader during copy so chunked uploads can't lie). SQLite itself is not a constraint either way; the PVC is the real cap for Option 1.
 - **MIME handling.** Security-critical (pentest #34 already fixed a content-type XSS on `/raw`). Rules:
  - Never trust the client-declared Content-Type. Sniff the first 512 bytes (`http.DetectContentType`), intersect with an allowlist.
  - Serve from a dedicated route (`/{id}/a/{n}`) with `Content-Type` from the stored *sniffed* type, `X-Content-Type-Options: nosniff`, `Content-Security-Policy: sandbox`, `Content-Disposition: attachment` unless the type is on a safe-inline allowlist (text/plain, images, PDF at user opt-in).
  - Never render user HTML/SVG inline (`image/svg+xml` is XSS-capable — serve as `attachment` always, or store sanitized).
 - **Streaming & serving.**
  - Filesystem: `http.ServeContent` on the opened file gives ranged GETs, ETag, Last-Modified for free.
  - MinIO: proxy via `GetObject` + `io.Copy` (simple, keeps auth checks in palette) or presigned GET (faster, but URL embeds credentials-temporarily and bypasses palette's per-request auth — wrong for pastes with passwords/burn semantics). Given cans inherit password/burn parity (#4), **proxying is required, which erodes MinIO's main serving advantage**.
 - **Lifecycle parity.** Attachments must honor soft-delete grace and sweep: sweeper hard-delete also removes blobs (files: `os.Remove`; S3: `DeleteObject`), best-effort with logging; orphan sweep job compares DB rows to store contents.
 ### Recommendation
 **Filesystem-on-volume first.** At current scale (single replica, PVC-based deploy, one user + homelab traffic) it is simpler end-to-end and keeps serving/auth/lifecycle in one place. The internal API should be a narrow blob interface (`Put(ctx, key, r io.Reader, size int64) / Open(key) / Delete(key)`) — about 60 lines per backend — so **MinIO becomes a drop-in later** if attachments outgrow the volume. That's the honest middle path: filesystem default, S3-ready seam, no MinIO dependency until it pays for itself.
 ## Part B — SQLite vs Postgres vs Redis (#31)
 ### Assessment of SQLite at pastebin scale
 - **Driver**: modernc.org/sqlite (pure Go, no cgo) — slightly slower than mattn/go-sqlite3 but fine; single-writer semantics are the real constraint, not driver speed.
 - **Access pattern**: paste-heavy, write-rare/read-often; primary keys and small set of indexes (visibility+created, expires, deleted); no joins beyond can items. This is SQLite's best case.
 - **WAL mode** is already on (`journal_mode(WAL), busy_timeout(5000)`) — concurrent readers don't block the single writer.
 - **Numbers**: SQLite comfortably handles millions of rows and hundreds of reads/sec; WAL write throughput is thousands of small inserts/sec. A pastebin doing even 100k pastes (avg 10 KB = ~1 GB DB) is trivial. Reads: prepared `WHERE id=?` lookups at this size are sub-millisecond.
 - **Weak points to watch** (document, none urgent):
  1. Single writer — heavy concurrent create traffic serializes. Mitigation: already rate-limited (#2); fine until that's the bottleneck (unlikely).
  2. `LENGTH(content)` on every list row — fine now; if it shows up in profiling, store `size` as a column (schema already has a `Size` field; list queries could use it).
  3. Sweeper runs a table-wide `UPDATE`+`DELETE` on tick — indexed, fine.
  4. No network access to the DB file — locks palette to single-replica. Acceptable: current deploy is one replica.
 - **Redis is the wrong tool** here: it's a cache/queue, not a system of record. Pastes are durable data with expiry semantics already implemented in SQLite. Redis would only add an optional read-cache layer for hot pastes — pure complexity for zero measured need.
 ### Should we build a backend abstraction (SQLite default, optional Postgres)?
 Arguments for: multi-replica scaling later; "docker image env choice" sounds nice; Postgres gives real concurrency and network access.
 Arguments against: a `Store` interface covering the current query surface is a real refactor (sqlite-flavored SQL: `INSERT OR IGNORE`-style upserts, partial indexes, `?` placeholders are compatible but behaviors differ — e.g. `sqlite` driver pragmas, transaction isolation, `AUTOINCREMENT` semantics); two backends means two test matrices and two migration paths forever; and there is **no current need** — single replica, single writer, modest data.
 **Recommendation: stay SQLite-only. Do not build the abstraction now.**
 Specifically:
 1. Keep all persistence behind `internal/store` (already done in #35 — the package boundary *is* the abstraction, at zero cost).
 2. Avoid SQLite-specific SQL going forward where free (standard placeholders, no `RETURNING` quirks) — cheap discipline that keeps a future port honest.
 3. Define the trigger conditions for revisiting, and write them down:
   - multiple replicas needed (scale-out), or
   - sustained WAL write contention (busy timeouts observed in logs), or
   - DB file > ~5-10 GB, or
   - a concrete user request for a Postgres-backed image.
 4. When a trigger fires, port `internal/store` to Postgres behind an interface extracted *then* — the refactor is mechanical against a real need, instead of speculative complexity now.
 5. For the docker image: `PALETTE_DB_PATH` env already implies the deployment choice; no extra backend knob needed.
 ## Summary
 | Decision | Choice |
 |---|---|
 | Attachment backend | Filesystem on PVC, behind a ~3-method blob interface; MinIO as a later drop-in, not a dependency |
 | Size limits | `max_attachment_bytes` admin setting, default 10 MiB, enforced pre-read + during stream |
 | MIME | Server-side sniff (512 bytes) + allowlist; `nosniff`, CSP `sandbox`, `Content-Disposition: attachment` except safe-inline types; SVG never inline |
 | Database | SQLite (WAL, modernc) only; no Postgres/Redis, no backend abstraction until a written trigger fires |
@@ -0,0 +1,160 @@
 # Design: Cookie-Based Preferences and Access Keys (#30)
 Status: design note — no implementation yet.
 Related: #37 (vwr viewer cookie), #34 (HMAC unlock cookie), #26 (creator auto-unlock), #36 (settings gear).
 ## Current cookie surface
 | Cookie | Purpose | Lifetime | Flags today |
 |---|---|---|---|
 | `vwr` | Anonymous viewer id; scopes `/mine` history and burn-after-N per-viewer dedupe; client-sent `vwr` also authorizes delete | 1 year | `HttpOnly`, `SameSite=Lax`, `Path=/` |
 | `pw_<id>` | Per-paste password unlock token = HMAC(paste id, PALETTE_UNLOCK_SECRET) | 1 hour | `HttpOnly`, `SameSite=Lax`, `Path=/` |
 | `tok_<id>` | One-time deletion-token handoff after create | 60 s | `HttpOnly`, `SameSite=Lax`, `Path=/` |
 The access-key feature is an extension of the `pw_<id>` pattern, not a new mechanism.
 ## Part 1: Preference storage
 ### What settings
 Only settings the *creator* sets when writing a paste, so the "new paste" form
 can pre-fill them:
 - Default language (`lang`)
 - Default expiry (`expires_in` / custom expiry)
 - Burn-after-N-reads default
 - Password-protect-by-default toggle (checkbox pre-checked; the password itself is never stored)
 - Default visibility of the "raw" link, if such a toggle exists
 - Collapsed/expanded state of the settings gear panel itself
 Never stored in cookies: passwords, access keys for pastes the user hasn't
 unlocked, deletion tokens (beyond the existing 60 s `tok_` handoff), anything
 typed into the paste body or title fields (existing rule: auto-detect must not
 overwrite user-typed content).
 ### One cookie, not many
 A single `prefs` cookie holding a compact JSON object:
 ```
 prefs={"lang":"go","exp":"1h","burn":0,"pw":1}
 ```
 - One cookie avoids the browser per-domain cookie count (typically 50+ per
  domain; Chrome 180) eating the budget that per-paste access-key cookies need.
 - Per-paste cookies (`pw_<id>`) are inherently name-per-paste and cannot be
  consolidated — that's the constraint that makes a single `prefs` cookie
  mandatory rather than stylistic.
 ### Size limits
 - RFC 6265: user agents SHOULD support at least 4096 bytes per cookie. Keep
  `prefs` under 256 bytes of JSON — it holds a handful of short enum values.
 - Server behavior: if the cookie is present but oversized/invalid JSON, ignore
  it silently and serve defaults. Never reject a request over a bad preference
  cookie.
 - Validate on the server (allowlist of known values); a cookie is untrusted
  input like any header.
 ### Flags
 `HttpOnly; SameSite=Lax; Path=/; Max-Age=31536000; Secure` (Secure once the
 prod instance serves HTTPS — it will, behind the letsencrypt IngressRoute;
 dev on plain HTTP needs the flag conditional on config).
 Preferences are not sensitive, but `HttpOnly` costs nothing and keeps script
 from mutating them; `SameSite=Lax` matches the existing cookies.
 ## Part 2: Access-key cookies
 ### Goal
 "Remember unlocked pastes on this browser" — after entering a password (or
 after creating a private paste), subsequent visits skip the unlock form. This
 extends `pw_<id>` from a 1-hour session convenience to a durable capability.
 ### Design: extend `pw_<id>`, don't invent a new scheme
 The token is already HMAC(paste id, PALETTE_UNLOCK_SECRET) — unforgeable and
 per-paste (fix for the #34 bypass). Changes:
 1. **Opt-in checkbox on the unlock form** ("remember on this browser") and a
   matching checkbox/note at creation time. Default OFF. Non-consenting
   visitors keep the current 1-hour cookie.
 2. **Extended lifetime** when opted in: `Max-Age = min(paste expiry, 90 days)`.
   The cookie must never outlive the paste — derive the cap from the paste's
   `ExpiresAt` at unlock time. Burn-after-N pastes: cap short (e.g. 24 h),
   since the paste may burn at any read.
 3. **Name collision**: paste ids are fixed-length server-generated, so
   `pw_<id>` names stay bounded (~40 bytes each). With the 50-cookies-per-
   domain budget, cap remembered pastes at ~30: when minting the 31st, drop
   the oldest expired-paste cookies server-side (server knows which ids are
   expired/deleted; send expired `Set-Cookie` with `Max-Age=0` to reclaim).
 4. **Delete authorization interplay**: today a client-sent `vwr` matching the
   paste's ViewerID authorizes delete. Access-key cookies grant *read*
   capability only. Do not let a `pw_<id>` cookie authorize deletion — that
   would mean cookie theft escalates from "read a paste" to "destroy it".
   Delete stays bound to `vwr` or the deletion token.
 ### Scoping
 - Keep `Path=/` (paste URLs are `/{id}` at the root; per-paste `Path=/{id}`
  would work but saves nothing and complicates cleanup).
 - Per-paste scope via the cookie *name* is the existing, tested pattern —
  no shared "access key ring" cookie. A consolidated `keys` cookie would
  mean one stolen cookie exposes every remembered paste at once.
 ## Part 3: Security considerations (honest accounting)
 - **XSS exfiltration**: `HttpOnly` prevents JS from *reading* the cookies, but
  not from *using* them — an XSS payload can simply `fetch('/<paste-id>')` and
  exfiltrate the content through the page the cookie unlocks. HttpOnly raises
  the bar (drive-by script can't dump the jar to an attacker server in one
  request), it does not make access-key cookies safe. This is a real
  limitation, not a solved problem. Mitigations in order of value:
  1. Fix the stored-XSS class at the source — #34 already allowlisted
     content-types on `/raw`; the standing debt items (CSP, X-Frame-Options,
     Referrer-Policy) directly reduce cookie-use exfiltration and should land
     before or with this feature.
  2. Keep access-key cookies opt-in, so the blast radius is bounded to users
     who accepted the tradeoff.
 - **Cookie theft = paste access**: anyone holding `pw_<id>` can read that
  paste until the cookie or paste expires, from any machine. That is inherent
  to capability cookies. Consequences accepted deliberately: pastes here are
  ephemeral (1 min–1 yr expiry), passwords are low-stakes share convenience,
  and there are no user accounts to compromise. Document this in the UI copy
  ("stores unlock access on this browser").
 - **Shared machines**: a remembered cookie defeats the password for the next
  user of the browser. The opt-in checkbox with plain-language copy is the
  mitigation; do not default it on.
 - **Cookie tossing / fixation**: a subdomain attacker could try to force
  cookies; palette is a single host, no untrusted subdomains. `SameSite=Lax`
  blocks cross-site attachment of the cookies on form posts to unlock
  endpoints.
 - **Multi-instance / secret rotation**: tokens are HMACs under
  `PALETTE_UNLOCK_SECRET`; rotating the secret silently invalidates all
  remembered cookies (acceptable — next visit re-prompts). Both dev and prod
  k3s instances need the same secret only if sharing a domain, which they do
  not.
 - **Preferences cookie**: not security-sensitive, but still validate/allowlist
  server-side to avoid it becoming an injection sink into templates.
 ## Recommendation
 Implement in two small, separately reviewable pieces:
 1. **`prefs` cookie** (do first, low risk): single JSON cookie < 256 bytes,
   server-validated allowlist, `HttpOnly; SameSite=Lax; Max-Age=1y`, drives
   only form pre-fill. Ship with #36's settings gear.
 2. **Extended `pw_<id>` opt-in** (second, security-sensitive): opt-in checkbox,
   Max-Age capped by paste expiry (90-day ceiling, 24 h for burn pastes),
   oldest-cookie eviction at ~30 pastes, no delete authorization from access
   cookies, and land the CSP/X-Frame-Options hardening debt from #34 in the
   same or preceding change. UI copy must disclose that the cookie preserves
   paste access on the browser.
 Rejected alternatives: single consolidated access-key cookie (aggregate theft
 risk, and the per-domain cookie-count argument cuts the other way for keys —
 consolidation maximizes what one stolen cookie unlocks); localStorage for
 preferences (XSS-readable, no benefit over HttpOnly cookies here); server-side
 accounts/session table (out of scope — Palette is deliberately anonymous).
@@ -0,0 +1,223 @@
 # Design: Optional client-side E2E encryption for pastes and files
 - **Issue:** #39
 - **Status:** Design (no implementation in this PR)
 - **Related docs:** [docs/API.md](../API.md)
 ## 1. Goals and non-goals
 **Goals**
 - Let any paste (or can item) be stored server-side as ciphertext only.
 - Zero plaintext knowledge by the server: storage, logs, backups, DB dumps contain no readable content.
 - Pure browser implementation using WebCrypto; no new server dependencies.
 - Encrypted pastes must still work with expiry, hard/soft delete, deletion tokens, visibility, slugs, rate limits.
 **Non-goals (v1)**
 - Anonymous, account-less E2E; Palette stays server-trusting with browser cookies.
 - Sharing via link fragments (`#key`) is optional sugar, not a required transport.
 - Search *of encrypted content*, server-side language detection, or server-side highlighting on encrypted pastes — these are structurally impossible and out of scope (see §5).
 - Signing, deniability, forward secrecy across pastes, PFS, post-quantum crypto.
 **Threat model (explicit).** This protects against a *passive server compromise* — a DB dump, backup leak, or disk image of the server's SQLite file. It does **not** protect against:
 - A fully malicious / compromised Palette server serving backdoored JavaScript: any JS-delivered crypto can be backdoored (key exfiltration via JS) regardless of primitives. This is the fundamental limit of a JS-in-browser E2E scheme.
 - Malware on the viewer's device, or shoulder-surfing of the password.
 - Traffic analysis, timing, or metadata (title, size, expiry, IP, viewer cookie).
 - A attacker who compromises the server *while the creator's browser is open* and alters JS before encrypt.
 Be explicit in user-facing copy: "encrypted at rest; the server cannot read your paste" is accurate — "the server can never see your paste" is not.
 ## 2. Crypto primitives and flow
 ### 2.1 Recommended parameters
 | Parameter | Recommendation | Notes |
 |---|---|---|
 | Cipher | **AES-256-GCM** | `AES-GCM` with a 256-bit key, per-paste random 96-bit IV/nonce. WebCrypto built-in, hardware-accelerated, authenticated. |
 | KDF | **PBKDF2-HMAC-SHA-256** | 600,000 iterations (OWASP 2023+ recommendation), 16-byte random salt. |
 | Argon2id | **Not in v1** | WebCrypto has no Argon2id; a JS/WASM Argon2 implementation is an extra supply-chain dependency and is an asymmetric liability: a script the server could swap can't be load-bearing for security anyway. Add later via `argon2id` WASM with SRI pinning + CSP (`script-src 'self'`) if needed. |
 | Salt | 16 random bytes per paste, stored in the clear alongside ciphertext | Unique per paste, never reused. |
 | IV | 12 random bytes per encryption | With ~2^32 encryptions per key this is negligible; each paste has its own key anyway. |
 | Key check value | See §2.2 | Catches wrong passwords without a server round-trip and prevents trash writes. |
 ### 2.2 Flow (create)
 1. User checks "Encrypt" and enters an encryption passphrase (distinct from any access password) in `/new`.
 2. Browser generates `salt` (16 B) and `iv` (12 B) via `crypto.getRandomValues`.
 3. `crypto.subtle.importKey("raw", passphrase, "PBKDF2", false, ["deriveKey"])` →
   `crypto.subtle.deriveKey(PBKDF2-SHA-256, 600k iterations, salt, {name:"AES-GCM", length:256}, false, ["encrypt","decrypt"])`.
 4. Generate a 32-byte random **DEK** (`crypto.getRandomValues(32)`).
 5. Content encryption key check: `iv_ckv`, `encrypted_content = AES-GCM-256(DEK, iv, content)`.
 6. **Key check value (KCV):** compute `AES-GCM-DEK(random 16 bytes)` — a small token encrypted *under the DEK*, stored as `key_check` blob. This is decrypted with the derived key; on wrong password GCM auth fails and the client can show "wrong key" without asking the server to burn a read.
 7. Wrap the DEK with the KEK: `wrapped_dek = AES-GCM(KEK, iv_wrap, dek)`.
 8. The stored envelope format:
   ```
   {
     v: 1, kdf: "PBKDF2-SHA256", iterations: 600000, salt_b64, iv_b64,
     kdf_salt_b64, wrap_iv_b64, wrapped_dek_b64, key_check_b64, ciphertext_b64
   ```
   The `v` field allows migrating to Argon2id later without a breaking change.
 8. POST the envelope (base64) as `content`, with an `encryption` metadata object alongside (see §3.1).
 ### 2.3 Flow (view)
 1. User provides the passphrase via form field, or the key arrives in the URL `#fragment`. The encryption passphrase is a separate field from any access password.
 2. Fetch `/api/pastes/{id}` (with access password in the usual field if the paste is also password-gated).
 3. Derive KEK from passphrase+salt, unwrap DEK via key_check / unwrap step.
 4. Decrypt content with the DEK; on `OperationError` → "wrong passphrase" UI state (retries are client-side only; no re-fetch, so no extra burn-after-read charge).
 5. Language detection happens client-side (e.g. highlight.js auto-detect) on the decrypted plaintext.
 ### §2.4 File and can items
 Files in cans: encrypt each file with its own DEK and store the same envelope. Cans' `json_items` content fields each carry their own envelope. Files keep their mime type in cleartext metadata; only the bytes are encrypted. The can's title stays plaintext (unless the whole can is encrypted, v2).
 ## 3. API shapes
 ### 3.1 Create request
 Existing fields unchanged. New optional `encryption` object:
 ```json
 POST /api/pastes
 {
  "content": "<base64 envelope>",
  "encryption": {"v": 1, "kdf": "PBKDF2-SHA256", "iterations": 600000,
                 "salt": "b64", "iv": "b64", "key_check": "b64"}
 }
 ```
 `encryption` is non-secret KDF metadata for UI display; the server treats `content` as opaque bytes and MUST NOT inspect it for encrypted pastes (no detection, no highlighting prep, no search indexing) — enforced where content is written, not per-handler.
 The full envelope can also just live inside `content` (server-opaque); the `encryption` object carries only non-secret KDF metadata the list views need (e.g. to show a 🔒 icon).
 ### 3.2 Create response
 Unchanged shape: `id`, `url`, `raw_url`, `api_url`, and the one-time `deletion_token` documented in docs/API.md.
 ### 3.3 Get response
 `GET /api/pastes/{id}` response gains:
 ```json
 {
  "id": "abc123",
  "content": "BASE64_ENVELOPE",
  "encryption": {"v":1, "kdf": "PBKDF2-SHA256", "iterations": 601570, "salt": "b64", "iv": "base64", "key_check": "b64"},
  "reads_remaining": null
 }
 ```
 `language` is `"encrypted"` or `null` so clients don't run detection on ciphertext. `raw_url` also serves the envelope; the `/{id}` page ships it to the browser, which decrypts in place.
 ### 3.4 Raw endpoint
 `GET /raw/{id}` returns the envelope as `application/octet-stream` with a suggested filename like `{id}.e2e.txt` and `Content-Disposition: attachment`. This is deliberate: a "download encrypted blob" is what a non-browser client can do with it anyway.
 ### 3.5 List views / mine / public
 List endpoints return `has_encryption: true` instead of content; show a lock icon. Do not include ciphertext in list responses (size, and no reason to ship ciphertext to every viewer's list view) — `GET /api/pastes/{id}` remains the only endpoint that returns the envelope.
 `/api/mine` (creator's own browser) may include the envelope for convenience; `/api/public` returns metadata only.
 `/api/guess-language` rejects encrypted content with `400 "content is client-encrypted"` — detection needs plaintext; clients detect after decrypting.
 Delete, redeem, rate limits, expiry, sweeper, deletion tokens, visibility, slugs, and can CRUD are unchanged — the server never inspects content for these, so opaque content is a no-op path.
 ## 4. Interplay with existing features
 | Feature | Impact | Mitigation |
 | Burn-after-read | Budget is charged on fetch, exactly as today; the server cannot know whether decryption succeeded, so a viewer fetching with the wrong key burns a read they can't use. | Decrypt retries are client-side, so only the first fetch charges the budget. Clear UX copy. |
 | Password-protected + encrypted | Both can coexist and are independent: the access password is an HTTP 401 gate; the encryption passphrase never leaves the browser. If both are set, all three secrets are needed (URL + access password + passphrase). Warn if the user enters the same value in both fields. |
 | Encryption-only pastes | Supported with no access password: URL + passphrase (or fragment key). Default is passphrase; fragment key is opt-in with a warning. |
 | Search | Structurally impossible over ciphertext. Server search just skips encrypted pastes; client-side search within a single decrypted paste works fine. No global encrypted-content search — accept the loss, document it. |
 | Language detection / highlighting | Server-side detection/highlighting impossible; returns `language: null`. Client-side detection via highlight.js auto-detect on decrypted plaintext (client already loads it for password gate pages). |
 | Cans/files | Per-item envelopes (own DEK each), per §2.4. | Consider a can-level KEK (one passphrase unlocks all items). |
 | Expiry/sweeper/delete/redeem | Unchanged — server never inspects content for these. |
 | List views (`/api/public`, `/api/mine`) | Additive `has_encryption: true` flag; list responses do not include ciphertext (`/api/mine` may include the envelope for the creator's own convenience). |
 | guess-language endpoint | Reject with 400. |
 | Fork / edit | Re-encryption needs the passphrase in the browser; v1 disables forking encrypted pastes. | Document the limitation. |
 ## 5. What breaks, stated plainly
 - **Search across encrypted pastes: impossible.** Accept the loss. (If ever needed, client-side index in IndexedDB for the creator's own pastes — v2+.)
 IndexedDB only helps the creator, not other viewers; still not global search. Accept the loss.
 - **Server-side language detection and highlighting: impossible.** Client-side detection on decrypted plaintext. Server returns `language: null` and the client detects.
 - **Burn-after-read is weakened in one specific way:** the budget is counted on fetch, not on successful decryption. A viewer who fetches but can't decrypt (wrong/lost key) burns a read they can't use. Mitigations documented in §4 table. The server can still count fetches (which is what burn-after-read actually is, even today: it counts fetches, not "reads" in any content-aware sense). So burn-after-read still works — it counts fetches — it's just that a failed decryption still consumes budget. This is acceptable and just needs UX copy. Optionally: don't decrement on failed decryption is *not possible* the server can't tell, so it's fetch-based, period. (It already is today.)
 - **Raw endpoint semantics change:** `/raw/{id}` can no longer serve readable raw text. It serves the ciphertext envelope. Scripts that curl raw pastes will get base64 envelope instead of text. Document as a breaking-ish change for encrypted pastes only; unencrypted pastes unchanged.
 - **Existing /api/mine, /api/public list shapes gain a flag** (additive, non-breaking).
 - **Copy-to-clipboard of decrypted text stays client-side**, fine. "Copy raw" on an encrypted paste copies the envelope — label it clearly.
 ## 5. UX for key sharing
 ### 5.1 Three sharing modes
 | Mode | What's shared | Security level | Use case |
 |---|---| malformed JSON / wrong key | | |
 | Mode | What's shared | Strength | Use case |
 |---|---|---|---|
 | **Passphrase** (default) | URL + passphrase out-of-band (Signal etc.) | Good — two channels | Team snippets, sensitive configs |
 | **Passphrase + access password** | URL + access password (401 gate) + passphrase | Strong — two secrets, two channels | Highest sensitivity |
 | **Random key in `#fragment`** | URL containing `#key=<b64>` | Weak — single channel; anyone with the full URL has both parts. Copy/paste into chat defeats it entirely. | One-click convenience sharing |
 Browsers never transmit `#` fragments to servers; still set `Referrer-Policy: no-referrer` site-wide and offer separate copy buttons for URL and key. Key-in-fragment ships with a warning and stays opt-in.
 ### 5.2 Create page (`/new`) UX
 - "Encrypt content" toggle → reveals passphrase field + strength meter + generate-random-key button.
 - When encrypting, hide the server-side language dropdown; the client detects language after decryption.
 - Two separate inputs with distinct labels: "Access password (checked by the server, 401 gate)" and "Encryption passphrase (never leaves your browser)". If both hold the same value, warn.
 ### 6.2 View page (`/{id}`) UX
 - If `encryption.kdf` is present → show key entry UI (after the access-password 401 gate, if that also applies).
 - After decrypt: normal render pipeline, language detected client-side.
 - "Wrong passphrase" retries never re-fetch, so they never burn extra reads.
 ## 7. Backwards compatibility and migration
 - Additive JSON fields only; unencrypted pastes behave identically. No schema changes (envelope is stored in the existing content column/TEXT; verify column size allows envelope overhead (~2× base64 + ~200 B header).
 - Server-side validation of encrypted pastes: only structural checks (base64 decodes, size ≤ max bytes). No crypto in the server.
 **Server implementation cost is genuinely small** (est. 2-4 days): pass through content untouched, add `encryption` metadata column or embed in content, skip detection/indexing when `encryption` is present, list flag. The server never does crypto. All crypto is client-side JS (~150-300 lines, no build-step change if using WebCrypto alone).
 **Argon2id later:** add `kdf: "argon2id"` to the envelope `v: 1` (m=64 MiB, t=3, p=1) via a SRI-pinned WASM module, with CSP `script-src 'self'` + SRI on the script tag. Envelope `v` field already allows this.
 ## 8. Recommendation
 **Build it, as an opt-in checkbox, passphrase mode only in v1.**
 - Server cost is small (pass-through + skip detection/indexing + list flag), client cost moderate (WebCrypto only, no new deps).
 - It closes the biggest real-world risk for a public pastebin: a DB/backup leak exposing every paste ever written.
 - Skip Argon2id in v1; envelope `v` field provides a migration path.
 - Key-in-fragment mode: build the plumbing (fragment parsing) but hide behind "advanced"; default remains passphrase.
 **Do not build:** server-side search over encrypted content, server-side highlighting of encrypted content, decrypt-on-server "preview" mode, or any server-side crypto.
 ## 9. Open questions
 1. Size limits: base64 expansion (~4/3×) plus ~200 B envelope overhead; the existing max-bytes / 413 limit applies to the envelope bytes the server stores. Do not compress before encrypting (CRIME-style weaknesses).
 2. Fork/edit of encrypted pastes: disabled in v1, revisit.
 3. Should `/api/mine` include the full envelope in list view? Leaning yes (creator's own browser can decrypt); note the larger payload.
 4. Should there be a "verify passphrase" second field at create time (type-twice), or rely on the KCV check at view time? KCV at view time suffices; type-twice adds friction at create. Rely on KCV, skip type-twice.
 5. CSP/Referrer-Policy hardening: `Referrer-Policy: no-referrer` site-wide is worth doing regardless of this feature (it also benefits unencrypted pastes).
 6. Cans: per-item DEKs wrapped by a single can-level KEK (one passphrase unlocks all items) — better UX, slightly more envelope design work. Defer detail to implementation.
 ## 10. Alternatives considered
 | Alternative | Why not in v1 |
 |---|---|
 | Argon2id via WASM in v1 | Extra JS dependency the server could swap → can't be load-bearing; PBKDF2-600k is adequate for a pastebin. Defer. |
 | Server holds half a key (2-of-2 with server-held share) | Re-introduces server trust; defeats the purpose. |
 | age-format envelopes | Nice CLI interop but no WebCrypto-native support; adds a JS dependency. Defer. |
 | PGP / S-MIME | Poor browser UX; heavy dependencies. |
 | Server-side encryption with server-held keys | Not E2E; that's "encrypted at rest", already covered by disk-level encryption. |
 | PrivateBin-style fragment key only | Single-channel sharing is a footgun; keep passphrase as default. |
 | libsodium / tweetnacl | Solid but unnecessary; WebCrypto covers AES-GCM + PBKDF2 natively. |
 ## 11. References
 - OWASP Password Storage Cheat Sheet (PBKDF2 guidance): https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html
 - MDN WebCrypto: https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto
 - PrivateBin (prior art for fragment-key sharing): https://privatebin.info
 - 0bin, Hemmelig — other pastebin/secret E2E prior art.
@@ -172,6 +172,11 @@ func (a *apiServer) adminKeyOK(r *http.Request, key string) bool {
 func (a *apiServer) adminAuth(next http.HandlerFunc, key string) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		if !rateLimitAdmin(r) {
 			log.Printf("admin auth RATE LIMITED: %s %s from %s", r.Method, r.URL.Path, r.RemoteAddr)
 			writeRateLimited(w, 60)
 			return
 		}
 		if !a.adminKeyOK(r, key) {
 			log.Printf("admin auth FAILURE: %s %s from %s", r.Method, r.URL.Path, r.RemoteAddr)
 			writeErr(w, 401, "unauthorized")
@@ -0,0 +1,80 @@
 package api
 // #66: admin key attempts must be rate limited per IP (5/min), constant-time
 // compared, and failures logged. Hammering bad keys must yield 429s.
 import (
 	"net/http/httptest"
 	"strings"
 	"testing"
 )
 // TestAdminKeyRateLimited: burst of 5 bad-key attempts allowed (401), the 6th
 // gets 429, and even the correct key is blocked from that IP until refill.
 func TestAdminKeyRateLimited(t *testing.T) {
 	srv := newTestServer(t)
 	h := srv.routes()
 	reqIP := "10.7.7.1:1234"
 	var got429, retryAfter bool
 	var lastCode int
 	for i := 0; i < 10; i++ {
 		req := httptest.NewRequest("POST", "/admin/api/settings", nil)
 		req.RemoteAddr = reqIP
 		req.Header.Set("X-Admin-Key", "wrong-key")
 		rec := httptest.NewRecorder()
 		h.ServeHTTP(rec, req)
 		lastCode = rec.Code
 		if rec.Code == 429 {
 			got429 = true
 			retryAfter = rec.Header().Get("Retry-After") != ""
 			break
 		}
 	}
 	if !got429 {
 		t.Fatalf("expected 429 after hammering bad keys, last status %d", lastCode)
 	}
 	if !retryAfter {
 		t.Error("429 missing Retry-After header")
 	}
 	// Correct key from the same IP is also locked out.
 	req := httptest.NewRequest("POST", "/admin/api/settings", nil)
 	req.RemoteAddr = reqIP
 	req.Header.Set("X-Admin-Key", srv.adminKey)
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
 	if rec.Code != 429 {
 		t.Errorf("correct key after lockout: got %d, want 429", rec.Code)
 	}
 	// A different IP is unaffected.
 	req2 := httptest.NewRequest("POST", "/admin/api/settings", strings.NewReader(`{"rate_limit_burst":5,"rate_limit_per_minute":60,"max_content_bytes":1048576,"custom_slug_reservation_days":30,"burn_viewer_window_minutes":15}`))
 	req2.RemoteAddr = "203.0.113.9:1234"
 	req2.Header.Set("X-Admin-Key", srv.adminKey)
 	rec2 := httptest.NewRecorder()
 	h.ServeHTTP(rec2, req2)
 	if rec2.Code != 200 {
 		t.Errorf("correct key from another IP: got %d, want 200", rec2.Code)
 	}
 }
 // TestAdminKeyConstantTimeCompare: sanity check that the comparison is
 // constant-time (uses subtle.ConstantTimeCompare, not ==).
 func TestAdminKeyConstantTimeCompare(t *testing.T) {
 	srv := newTestServer(t)
 	r := httptest.NewRequest("GET", "/", nil)
 	r.Header.Set("X-Admin-Key", "test-admin-key")
 	if !srv.adminKeyOK(r, srv.adminKey) {
 		t.Fatal("correct key rejected")
 	}
 	r.Header.Set("X-Admin-Key", "wrong")
 	if srv.adminKeyOK(r, srv.adminKey) {
 		t.Fatal("wrong key accepted")
 	}
 	// differ in length: must not panic/mismatch unexpectedly
 	r.Header.Set("X-Admin-Key", "test-admin-key-longer")
 	if srv.adminKeyOK(r, srv.adminKey) {
 		t.Fatal("longer wrong key accepted")
 	}
 }
@@ -0,0 +1,45 @@
 package api
 import (
 	"net/http/httptest"
 	"testing"
 )
 // #60: the cans API must clamp expires_in at the boundary exactly like the
 // pastes API — reject zero/negative durations and anything over the 1-year
 // UI cap, accept the exact boundaries.
 func TestCreateCanExpiryBounds(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	cases := []struct {
 		expiresIn string
 		wantCode  int
 	}{
 		{"-1h", 400},    // negative
 		{"-0s", 400},    // negative zero
 		{"0s", 400},     // zero
 		{"1ns", 400},    // positive but below the 1-minute floor
 		{"59s", 400},    // just under the floor
 		{"1m", 201},     // exactly the floor
 		{"90s", 201},    // just over the floor
 		{"8760h", 201},  // exactly 1 year
 		{"8785h", 400},  // 1 year + 1 day: over the cap
 		{"87600h", 400}, // 10 years, the originally reported case
 	}
 	for _, c := range cases {
 		globalLimiter = newLimiter() // avoid create rate limit between cases
 		body, ct := multipartBody(t, map[string]string{
 			"json_items": `[{"title":"a.txt","content":"AAA"}]`,
 			"expires_in": c.expiresIn,
 		}, "files", "pic.txt", "file data")
 		req := httptest.NewRequest("POST", "/api/pastes/can", body)
 		req.Header.Set("Content-Type", ct)
 		rec := httptest.NewRecorder()
 		h.ServeHTTP(rec, req)
 		if rec.Code != c.wantCode {
 			t.Errorf("expires_in %q: got %d want %d (%s)",
 				c.expiresIn, rec.Code, c.wantCode, rec.Body.String())
 		}
 	}
 }
@@ -0,0 +1,198 @@
 package api
 // Regression tests for #68 input-validation gaps: negative/oversized content
 // lengths (413), limit=0 → default page size, unchecked query params
 // (negative offset), and negative burn_after_reads.
 import (
 	"encoding/json"
 	"fmt"
 	"net/http"
 	"net/http/httptest"
 	"strings"
 	"testing"
 )
 func createPasteRaw(t *testing.T, h http.Handler, body string) *httptest.ResponseRecorder {
 	t.Helper()
 	req := httptest.NewRequest("POST", "/api/pastes", strings.NewReader(body))
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
 	return rec
 }
 // A request whose decoded content exceeds the admin-tunable cap is rejected
 // with 413 and a clear message (content under the body cap, over the
 // content cap).
 func TestCreatePasteContentOverCap413(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	// content over MaxContentBytes (5MiB) but under body cap (+4KiB): send
 	// just over the content cap so the per-field check fires first.
 	content := strings.Repeat("a", 5*1024*1024+10)
 	rec := createPasteRaw(t, h, fmt.Sprintf(`{"content":"%s"}`, content))
 	if rec.Code != http.StatusRequestEntityTooLarge {
 		t.Fatalf("got %d want 413: %s", rec.Code, rec.Body.String())
 	}
 	if !strings.Contains(rec.Body.String(), "content exceeds max") {
 		t.Fatalf("unclear error message: %s", rec.Body.String())
 	}
 }
 // A request whose entire body is larger than the server-side body cap is cut
 // off by http.MaxBytesReader and answered with 413, not decoded into memory
 // (#68: previously a giant body was fully buffered, then rejected only at
 // the per-field check — actually the decode happened before any check).
 func TestCreatePasteBodyOverCap413(t *testing.T) {
 	s := testServer(t)
 	// shrink the content cap so the body cap is small too
 	ss := s.settings.get()
 	ss.MaxContentBytes = 64 * 1024
 	if err := s.settings.set(ss); err != nil {
 		t.Fatal(err)
 	}
 	h := s.routes()
 	content := strings.Repeat("a", 200*1024) // 200KiB > 64KiB+4KiB body cap
 	rec := createPasteRaw(t, h, fmt.Sprintf(`{"content":"%s","title":"x"}`, content))
 	if rec.Code != http.StatusRequestEntityTooLarge {
 		t.Fatalf("got %d want 413: %s", rec.Code, rec.Body.String())
 	}
 }
 // Negative content lengths cannot be expressed via JSON, but a negative
 // expires-style numeric payload must not crash; more importantly the
 // burn_after_reads field: negative values are rejected with a clear message.
 func TestCreatePasteNegativeBurnAfterReads(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	rec := createPasteRaw(t, h, `{"content":"hi","burn_after_reads":-5}`)
 	if rec.Code != http.StatusBadRequest {
 		t.Fatalf("got %d want 400: %s", rec.Code, rec.Body.String())
 	}
 	if !strings.Contains(rec.Body.String(), "burn_after_reads") {
 		t.Fatalf("unclear error message: %s", rec.Body.String())
 	}
 	// 0 and positive values still work (0 = default single read, per #49)
 	rec = createPasteRaw(t, h, `{"content":"hi","burn_after_reads":0,"burn_after_read":true}`)
 	if rec.Code != http.StatusCreated {
 		t.Fatalf("zero burn_after_reads: got %d want 201: %s", rec.Code, rec.Body.String())
 	}
 }
 // limit=0 on list endpoints returns the default page size (existing clamp
 // treats <=0 as default; #68 asks this be explicit and tested).
 func TestListLimitZeroUsesDefault(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	// seed 3 public pastes
 	for i := 0; i < 3; i++ {
 		rec := createPasteRaw(t, h, fmt.Sprintf(`{"content":"p%d"}`, i))
 		if rec.Code != 201 {
 			t.Fatalf("seed: got %d: %s", rec.Code, rec.Body.String())
 		}
 	}
 	for _, q := range []string{"/api/public?limit=0", "/api/public"} {
 		req := httptest.NewRequest("GET", q, nil)
 		rec := httptest.NewRecorder()
 		h.ServeHTTP(rec, req)
 		if rec.Code != 200 {
 			t.Fatalf("%s: got %d", q, rec.Code)
 		}
 		var got struct {
 			Limit int                   `json:"limit"`
 			Total int                   `json:"total"`
 			Items []struct{ ID string } `json:"items"`
 		}
 		json.Unmarshal(rec.Body.Bytes(), &got)
 		if got.Limit != 25 || len(got.Items) != 3 {
 			t.Fatalf("%s: limit=%d items=%d, want limit 25 and all 3 items", q, got.Limit, len(got.Items))
 		}
 	}
 }
 // Huge limit values are clamped to the max page size (already the behavior;
 // regression-tested here per #68 "validate unchecked params").
 func TestListLimitHugeClamped(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	req := httptest.NewRequest("GET", "/api/public?limit=999999999", nil)
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
 	var got struct {
 		Limit int `json:"limit"`
 	}
 	json.Unmarshal(rec.Body.Bytes(), &got)
 	if got.Limit != 25 {
 		t.Fatalf("limit=%d, want clamped to 25", got.Limit)
 	}
 }
 // Negative offset previously passed through unchecked to SQL (harmless in
 // SQLite, but invalid); it must be clamped to 0 (#68).
 func TestListNegativeOffsetClamped(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	for i := 0; i < 2; i++ {
 		rec := createPasteRaw(t, h, fmt.Sprintf(`{"content":"p%d"}`, i))
 		if rec.Code != 201 {
 			t.Fatalf("seed: got %d", rec.Code)
 		}
 	}
 	req := httptest.NewRequest("GET", "/api/public?offset=-999", nil)
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
 	if rec.Code != 200 {
 		t.Fatalf("got %d", rec.Code)
 	}
 	var got struct {
 		Offset int `json:"offset"`
 		Total  int `json:"total"`
 	}
 	json.Unmarshal(rec.Body.Bytes(), &got)
 	if got.Offset != 0 || got.Total != 2 {
 		t.Fatalf("offset=%d total=%d, want offset 0 and total 2", got.Offset, got.Total)
 	}
 	// /api/mine too (needs the viewer cookie)
 	req = httptest.NewRequest("GET", "/api/mine?offset=-5", nil)
 	req.AddCookie(&http.Cookie{Name: "vwr", Value: "offclamp"})
 	rec = httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
 	var mine struct {
 		Offset int `json:"offset"`
 	}
 	json.Unmarshal(rec.Body.Bytes(), &mine)
 	if mine.Offset != 0 {
 		t.Fatalf("mine offset=%d, want 0", mine.Offset)
 	}
 }
 // Non-numeric limit/offset fall back to defaults instead of 500s.
 func TestListGarbageParams(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	req := httptest.NewRequest("GET", "/api/public?limit=abc&offset=xyz", nil)
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
 	if rec.Code != 200 {
 		t.Fatalf("got %d", rec.Code)
 	}
 	var got struct {
 		Limit  int `json:"limit"`
 		Offset int `json:"offset"`
 	}
 	json.Unmarshal(rec.Body.Bytes(), &got)
 	if got.Limit != 25 || got.Offset != 0 {
 		t.Fatalf("limit=%d offset=%d, want 25/0", got.Limit, got.Offset)
 	}
 }
@@ -0,0 +1,92 @@
 package api
 // #81: ALL password verification attempts (GET query param, header, POST
 // form) must go through the per-IP unlock limiter. Regression: N wrong
 // passwords via GET ?password= must eventually yield 429.
 import (
 	"encoding/json"
 	"net/http/httptest"
 	"strings"
 	"testing"
 )
 func createPasswordPaste(t *testing.T, s *apiServer, pw string) string {
 	t.Helper()
 	h := s.routes()
 	body := `{"content":"secret","password":"` + pw + `"}`
 	req := httptest.NewRequest("POST", "/api/pastes", strings.NewReader(body))
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
 	var created struct {
 		ID string `json:"id"`
 	}
 	json.Unmarshal(rec.Body.Bytes(), &created)
 	return created.ID
 }
 // TestRateLimitGetPasswordQuery: repeated wrong passwords via GET
 // ?password= must eventually return 429 (unlock limiter: burst 5).
 func TestRateLimitGetPasswordQuery(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	id := createPasswordPaste(t, s, "hunter2")
 	var saw429 bool
 	// more attempts than the unlock burst (5)
 	for i := 0; i < 10; i++ {
 		req := httptest.NewRequest("GET", "/api/pastes/"+id+"?password=wrong"+string(rune('a'+i)), nil)
 		rec := httptest.NewRecorder()
 		h.ServeHTTP(rec, req)
 		if rec.Code == 429 {
 			saw429 = true
 			break
 		}
 		if rec.Code != 401 {
 			t.Fatalf("attempt %d: expected 401 before limit, got %d", i, rec.Code)
 		}
 	}
 	if !saw429 {
 		t.Fatal("expected 429 after repeated wrong ?password= attempts, never got one")
 	}
 }
 // TestRateLimitGetPasswordHeader: same guarantee for the X-Paste-Password header path.
 func TestRateLimitGetPasswordHeader(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	id := createPasswordPaste(t, s, "hunter2")
 	var saw429 bool
 	for i := 0; i < 10; i++ {
 		req := httptest.NewRequest("GET", "/api/pastes/"+id, nil)
 		req.Header.Set("X-Paste-Password", "wrong"+string(rune('a'+i)))
 		rec := httptest.NewRecorder()
 		h.ServeHTTP(rec, req)
 		if rec.Code == 429 {
 			saw429 = true
 			break
 		}
 		if rec.Code != 401 {
 			t.Fatalf("attempt %d: expected 401 before limit, got %d", i, rec.Code)
 		}
 	}
 	if !saw429 {
 		t.Fatal("expected 429 after repeated wrong header password attempts, never got one")
 	}
 }
 // TestRateLimitGetPasswordCorrectStillAllowed: a correct password must still
 // work within the burst (the limiter gates attempts, not correctness).
 func TestRateLimitGetPasswordCorrectStillAllowed(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	id := createPasswordPaste(t, s, "hunter2")
 	req := httptest.NewRequest("GET", "/api/pastes/"+id+"?password=hunter2", nil)
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
 	if rec.Code != 200 {
 		t.Fatalf("expected 200 for correct password within burst, got %d", rec.Code)
 	}
 }
@@ -0,0 +1,152 @@
 package api
 // Regression tests for #86: title and language are bounded at create time.
 // Titles over 200 chars are truncated; language must match
 // ^[a-zA-Z0-9+#-]{1,40}$ or the create is rejected with a clear 400.
 import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
 	"strings"
 	"testing"
 )
 // pasteMeta fetches a created paste's stored metadata via the API.
 func pasteMeta(t *testing.T, h http.Handler, id string) map[string]any {
 	t.Helper()
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, httptest.NewRequest("GET", "/api/pastes/"+id, nil))
 	if rec.Code != 200 {
 		t.Fatalf("get paste %s: got %d: %s", id, rec.Code, rec.Body.String())
 	}
 	var m map[string]any
 	if err := json.Unmarshal(rec.Body.Bytes(), &m); err != nil {
 		t.Fatal(err)
 	}
 	return m
 }
 // A 5000-char title is truncated to 200 characters at create time (#86).
 func TestCreatePasteTitleTruncated(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	title := strings.Repeat("t", 5000)
 	body, _ := json.Marshal(map[string]any{"content": "hi", "title": title})
 	rec := createPasteRaw(t, h, string(body))
 	if rec.Code != http.StatusCreated {
 		t.Fatalf("got %d want 201: %s", rec.Code, rec.Body.String())
 	}
 	var resp struct {
 		ID string `json:"id"`
 	}
 	json.Unmarshal(rec.Body.Bytes(), &resp)
 	meta := pasteMeta(t, h, resp.ID)
 	got, _ := meta["title"].(string)
 	if got != strings.Repeat("t", 200) {
 		t.Fatalf("title not truncated to 200 chars: len=%d", len(got))
 	}
 }
 // A title within the 200-char bound is stored verbatim (minus surrounding
 // whitespace, which is trimmed).
 func TestCreatePasteTitleWithinBoundKept(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	title := "  " + strings.Repeat("x", 200) + "  "
 	body, _ := json.Marshal(map[string]any{"content": "hi", "title": title})
 	rec := createPasteRaw(t, h, string(body))
 	if rec.Code != http.StatusCreated {
 		t.Fatalf("got %d want 201: %s", rec.Code, rec.Body.String())
 	}
 	var resp struct {
 		ID string `json:"id"`
 	}
 	json.Unmarshal(rec.Body.Bytes(), &resp)
 	meta := pasteMeta(t, h, resp.ID)
 	if got, _ := meta["title"].(string); got != strings.Repeat("x", 200) {
 		t.Fatalf("title changed unexpectedly: len=%d", len(got))
 	}
 }
 // A language longer than 40 chars is rejected with a clear 400 (#86).
 func TestCreatePasteLanguageTooLong400(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	body, _ := json.Marshal(map[string]any{"content": "hi", "language": strings.Repeat("a", 41)})
 	rec := createPasteRaw(t, h, string(body))
 	if rec.Code != http.StatusBadRequest {
 		t.Fatalf("got %d want 400: %s", rec.Code, rec.Body.String())
 	}
 	if !strings.Contains(rec.Body.String(), "language") {
 		t.Fatalf("unclear error message: %s", rec.Body.String())
 	}
 }
 // Language strings outside ^[a-zA-Z0-9+#-]{1,40}$ are rejected with 400.
 func TestCreatePasteLanguageBadFormat400(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	for _, bad := range []string{
 		"<img src=x onerror=alert(1)>",
 		"java script",
 		"c++ extra!",
 		"py_thon",
 		"go.lang",
 	} {
 		body, _ := json.Marshal(map[string]any{"content": "hi", "language": bad})
 		rec := createPasteRaw(t, h, string(body))
 		if rec.Code != http.StatusBadRequest {
 			t.Errorf("language %q: got %d want 400: %s", bad, rec.Code, rec.Body.String())
 			continue
 		}
 		if !strings.Contains(rec.Body.String(), "language must match") {
 			t.Errorf("language %q: unclear error: %s", bad, rec.Body.String())
 		}
 	}
 }
 // Valid languages (letters, digits, #, +, -) within 40 chars are accepted.
 func TestCreatePasteLanguageValidAccepted(t *testing.T) {
 	for _, ok := range []string{"go", "c#", "f#", "c++", "objective-c", "ECMAScript-2023", strings.Repeat("a", 40)} {
 		s2 := testServer(t) // fresh rate limiter per case
 		h2 := s2.routes()
 		body, _ := json.Marshal(map[string]any{"content": "hi", "language": ok})
 		rec := createPasteRaw(t, h2, string(body))
 		if rec.Code != http.StatusCreated {
 			t.Errorf("language %q: got %d want 201: %s", ok, rec.Code, rec.Body.String())
 		}
 	}
 }
 // An absent or blank language still creates fine and stores NULL, and a
 // blank title is stored NULL rather than an empty string.
 func TestCreatePasteBlankMetadataOK(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	for _, body := range []string{
 		`{"content":"hi"}`,
 		`{"content":"hi","language":"","title":"  "}`,
 	} {
 		rec := createPasteRaw(t, h, body)
 		if rec.Code != http.StatusCreated {
 			t.Fatalf("body %s: got %d want 201: %s", body, rec.Code, rec.Body.String())
 		}
 		var resp struct {
 			ID string `json:"id"`
 		}
 		json.Unmarshal(rec.Body.Bytes(), &resp)
 		meta := pasteMeta(t, h, resp.ID)
 		if lang, ok := meta["language"]; ok && lang != nil && lang != "" {
 			t.Fatalf("body %s: language not null: %v", body, lang)
 		}
 		if title, ok := meta["title"]; ok && title != nil && title != "" {
 			t.Fatalf("body %s: title not null: %v", body, title)
 		}
 	}
 }
@@ -183,6 +183,46 @@ func TestListPublicExcludesUnlisted(t *testing.T) {
 	}
 }
 func TestListPublicExcludesPasswordAndUnlisted(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
 	bodies := []string{
 		`{"content":"open","visibility":"public"}`,
 		`{"content":"locked","visibility":"public","password":"hunter2"}`,
 		`{"content":"hidden","visibility":"unlisted"}`,
 	}
 	for _, body := range bodies {
 		req := httptest.NewRequest("POST", "/api/pastes", strings.NewReader(body))
 		rec := httptest.NewRecorder()
 		h.ServeHTTP(rec, req)
 		if rec.Code != 201 {
 			t.Fatalf("create %s: got %d", body, rec.Code)
 		}
 	}
 	req := httptest.NewRequest("GET", "/api/public", nil)
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, req)
 	if rec.Code != 200 {
 		t.Fatalf("list public: got %d", rec.Code)
 	}
 	var resp struct {
 		Total int              `json:"total"`
 		Items []map[string]any `json:"items"`
 	}
 	json.Unmarshal(rec.Body.Bytes(), &resp)
 	if resp.Total != 1 || len(resp.Items) != 1 {
 		t.Fatalf("expected only the 1 public paste, got total=%d items=%d", resp.Total, len(resp.Items))
 	}
 	// password-protected and unlisted pastes must not appear (no metadata leak)
 	for _, secret := range []string{"hunter2", "locked", "hidden"} {
 		if strings.Contains(rec.Body.String(), secret) {
 			t.Fatalf("leaked %q in /api/public response", secret)
 		}
 	}
 }
 func TestSweepSoftDeletesAfterGrace(t *testing.T) {
 	s := testServer(t)
 	h := s.routes()
@@ -0,0 +1,97 @@
 package api
 // #83 regression tests: `public` boolean in the create payload must map to
 // visibility (false -> unlisted, true -> public); string `visibility` still works.
 import (
 	"encoding/json"
 	"net/http/httptest"
 	"strings"
 	"testing"
 )
 func createPasteBody(t *testing.T, h *apiServer, body string) map[string]any {
 	req := httptest.NewRequest("POST", "/api/pastes", strings.NewReader(body))
 	rec := httptest.NewRecorder()
 	h.routes().ServeHTTP(rec, req)
 	if rec.Code != 201 {
 		t.Fatalf("create: got %d: %s", rec.Code, rec.Body.String())
 	}
 	var resp map[string]any
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("bad json: %v", err)
 	}
 	return resp
 }
 func getVis(t *testing.T, h *apiServer, id string) string {
 	req := httptest.NewRequest("GET", "/api/pastes/"+id, nil)
 	rec := httptest.NewRecorder()
 	h.routes().ServeHTTP(rec, req)
 	if rec.Code != 200 {
 		t.Fatalf("get %s: got %d", id, rec.Code)
 	}
 	var resp struct {
 		Visibility string `json:"visibility"`
 	}
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("bad json: %v", err)
 	}
 	return resp.Visibility
 }
 // TestPublicBooleanFalseMapsToUnlisted: {"public": false} must create an unlisted paste.
 func TestPublicBooleanFalseMapsToUnlisted(t *testing.T) {
 	s := testServer(t)
 	resp := createPasteBody(t, s, `{"content":"x","public":false}`)
 	if v := getVis(t, s, resp["id"].(string)); v != "unlisted" {
 		t.Fatalf("public:false -> got visibility %q, want unlisted", v)
 	}
 }
 // TestPublicBooleanTrueMapsToPublic: {"public": true} must create a public paste.
 func TestPublicBooleanTrueMapsToPublic(t *testing.T) {
 	s := testServer(t)
 	resp := createPasteBody(t, s, `{"content":"x","public":true}`)
 	if v := getVis(t, s, resp["id"].(string)); v != "public" {
 		t.Fatalf("public:true -> got visibility %q, want public", v)
 	}
 }
 // TestPublicBooleanOverridesString: boolean wins when both fields are sent.
 func TestPublicBooleanOverridesString(t *testing.T) {
 	s := testServer(t)
 	resp := createPasteBody(t, s, `{"content":"x","visibility":"public","public":false}`)
 	if v := getVis(t, s, resp["id"].(string)); v != "unlisted" {
 		t.Fatalf("boolean override -> got %q, want unlisted", v)
 	}
 }
 // TestVisibilityStringStillWorks: existing string contract unchanged.
 func TestVisibilityStringStillWorks(t *testing.T) {
 	s := testServer(t)
 	resp := createPasteBody(t, s, `{"content":"x","visibility":"unlisted"}`)
 	if v := getVis(t, s, resp["id"].(string)); v != "unlisted" {
 		t.Fatalf("string field -> got %q, want unlisted", v)
 	}
 	resp = createPasteBody(t, s, `{"content":"y","visibility":"public"}`)
 	if v := getVis(t, s, resp["id"].(string)); v != "public" {
 		t.Fatalf("string field -> got %q, want public", v)
 	}
 }
 // TestPublicListExcludesPublicFalse: {"public":false} pastes stay out of /api/public.
 func TestPublicListExcludesPublicFalse(t *testing.T) {
 	s := testServer(t)
 	createPasteBody(t, s, `{"content":"hidden","public":false}`)
 	req := httptest.NewRequest("GET", "/api/public", nil)
 	rec := httptest.NewRecorder()
 	s.routes().ServeHTTP(rec, req)
 	var resp struct {
 		Total int `json:"total"`
 	}
 	json.Unmarshal(rec.Body.Bytes(), &resp)
 	if resp.Total != 0 {
 		t.Fatalf("public:false paste leaked into /api/public: total=%d", resp.Total)
 	}
 }
@@ -48,8 +48,28 @@ func (l *limiter) allow(key string, rate, burst float64) bool {
 	return true
 }
-// clientIP extracts the request IP (no reverse proxy header by default).
+// clientIP extracts the client IP for rate-limit keying (#85).
 //
 // Trust boundary: palette runs behind exactly ONE trusted reverse proxy
 // (Traefik in the k3s pod network). Traefik APPENDS the real client IP to
 // X-Forwarded-For, so the RIGHTMOST entry is the last value the trusted
 // proxy observed and is unspoofable by the client (a client-supplied fake
 // entry only lands on the LEFT and is ignored). This matches chi's
 // middleware.RealIP semantics for a single trusted proxy hop.
 //
 // Direct connections (no XFF header) fall back to RemoteAddr. Directly
 // reachable deployments must NOT expose the app to untrusted networks
 // without a proxy in front, or attackers could forge the rightmost entry.
 func clientIP(r *http.Request) string {
 	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
 		if i := strings.LastIndex(xff, ","); i >= 0 {
 			return strings.TrimSpace(xff[i+1:])
 		}
 		return strings.TrimSpace(xff)
 	}
 	if xr := r.Header.Get("X-Real-Ip"); xr != "" {
 		return strings.TrimSpace(xr)
 	}
 	host := r.RemoteAddr
 	if i := strings.LastIndex(host, ":"); i > 0 {
 		host = host[:i]
@@ -84,6 +104,12 @@ func rateLimitUnlock(id string, r *http.Request) bool {
 	return globalLimiter.allow("unlock:"+id+":"+clientIP(r), 5.0/60.0, 5)
 }
 // rateLimitAdmin: 5 attempts per minute per IP on the admin key check (#66),
 // same pattern as the unlock limiter (#34).
 func rateLimitAdmin(r *http.Request) bool {
 	return globalLimiter.allow("admin:"+clientIP(r), 5.0/60.0, 5)
 }
 // writeRateLimited responds 429 with Retry-After based on refill rate.
 func writeRateLimited(w http.ResponseWriter, retryAfterSecs int) {
 	w.Header().Set("Retry-After", strconv.Itoa(retryAfterSecs))
@@ -0,0 +1,85 @@
 package api
 // Issue #85: the rate limit key must use the rightmost X-Forwarded-For entry
 // (appended by the trusted Traefik proxy), never the raw/leftmost header
 // value a client can forge. A spoofed FIRST XFF entry must not bypass the
 // limit or rotate buckets.
 import (
 	"bytes"
 	"net/http/httptest"
 	"testing"
 )
 func TestClientIPTakesRightmostXFF(t *testing.T) {
 	r := httptest.NewRequest("POST", "/", nil)
 	r.RemoteAddr = "10.42.0.7:51000" // trusted Traefik pod
 	r.Header.Set("X-Forwarded-For", "1.2.3.4, 1.2.3.5, 203.0.113.9")
 	if got := clientIP(r); got != "203.0.113.9" {
 		t.Fatalf("clientIP = %q, want rightmost 203.0.113.9", got)
 	}
 }
 func TestClientIPXRealIPFallback(t *testing.T) {
 	r := httptest.NewRequest("POST", "/", nil)
 	r.RemoteAddr = "10.42.0.7:51000"
 	r.Header.Set("X-Real-Ip", "203.0.113.10")
 	if got := clientIP(r); got != "203.0.113.10" {
 		t.Fatalf("clientIP = %q, want 203.0.113.10", got)
 	}
 }
 func TestClientIPDirectFallback(t *testing.T) {
 	r := httptest.NewRequest("POST", "/", nil)
 	r.RemoteAddr = "198.51.100.5:51000"
 	if got := clientIP(r); got != "198.51.100.5" {
 		t.Fatalf("clientIP = %q, want 198.51.100.5", got)
 	}
 }
 // TestRateLimitSpoofedFirstXFFDoesNotBypass: an attacker rotating a fake
 // leftmost XFF entry stays limited on their real (rightmost) IP.
 func TestRateLimitSpoofedFirstXFFDoesNotBypass(t *testing.T) {
 	srv := newTestServer(t)
 	h := srv.routes()
 	for i := 0; i < 5; i++ {
 		req := httptest.NewRequest("POST", "/api/pastes", bytes.NewReader([]byte(`{"content":"hi"}`)))
 		req.RemoteAddr = "10.42.0.7:51000"
 		// each request spoofs a DIFFERENT leftmost entry
 		req.Header.Set("X-Forwarded-For", spoofN(i)+", 203.0.113.9")
 		rr := httptest.NewRecorder()
 		h.ServeHTTP(rr, req)
 		if rr.Code != 201 {
 			t.Fatalf("req %d: want 201, got %d", i, rr.Code)
 		}
 	}
 	// 6th request, still the same real IP, new spoofed prefix: must 429
 	req := httptest.NewRequest("POST", "/api/pastes", bytes.NewReader([]byte(`{"content":"hi"}`)))
 	req.RemoteAddr = "10.42.0.7:51000"
 	req.Header.Set("X-Forwarded-For", "9.9.9.9, 203.0.113.9")
 	rr := httptest.NewRecorder()
 	h.ServeHTTP(rr, req)
 	if rr.Code != 429 {
 		t.Fatalf("spoofed 6th req: want 429, got %d", rr.Code)
 	}
 }
 func spoofN(i int) string {
 	return "1.2.3." + string(rune('0'+i))
 }
 // Distinct real IPs must still get distinct buckets (no over-limiting).
 func TestRateLimitDistinctRightmostIPsIndependent(t *testing.T) {
 	srv := newTestServer(t)
 	h := srv.routes()
 	for _, ip := range []string{"203.0.113.20", "203.0.113.21"} {
 		req := httptest.NewRequest("POST", "/api/pastes", bytes.NewReader([]byte(`{"content":"hi"}`)))
 		req.RemoteAddr = "10.42.0.7:51000"
 		req.Header.Set("X-Forwarded-For", "6.6.6.6, "+ip)
 		rr := httptest.NewRecorder()
 		h.ServeHTTP(rr, req)
 		if rr.Code != 201 {
 			t.Fatalf("ip %s: want 201, got %d", ip, rr.Code)
 		}
 	}
 }
@@ -60,7 +60,9 @@ func (a *apiServer) routes() http.Handler {
 	r := chi.NewRouter()
 	r.Use(middleware.Recoverer)
 	r.Use(middleware.Timeout(30 * time.Second))
 	r.Use(a.limitRequestBody) // #68: hard server-side body cap -> 413
 	r.Use(viewerCookieMiddleware)
 	r.Use(web.SecurityHeaders) // #59: CSP + hardening headers on HTML pages
 	// admin (#40): HTML page is open (key entry via form); API is key-guarded
 	r.Get("/admin", a.ui.Handlers().HandleAdminPage)
@@ -155,17 +157,44 @@ func (a *apiServer) handleCreatePaste(w http.ResponseWriter, r *http.Request) {
 	}
 	var p store.Paste
 	if err := json.NewDecoder(r.Body).Decode(&p); err != nil {
 		if isBodyTooLarge(err) { // #68: body cut off by MaxBytesReader
 			writeBodyTooLarge(w)
 			return
 		}
 		writeErr(w, 400, "invalid json body")
 		return
 	}
-	if strings.TrimSpace(p.Content) == "" {
+	if status, msg := checkContent(p.Content, s.MaxContentBytes); status != 0 {
-		writeErr(w, 400, "content is required")
+		writeErr(w, status, msg)
 		return
 	}
-	if int64(len(p.Content)) > s.MaxContentBytes { // #40: admin-tunable
+	// #86: bound free-form metadata at create time
-		writeErr(w, 413, fmt.Sprintf("content exceeds max %d bytes", s.MaxContentBytes))
+	if p.Title != nil {
 		t, err := checkTitle(*p.Title)
 		if err != nil {
 			writeErr(w, 400, err.Error())
 			return
 		}
 		p.Title = &t
 	}
 	if p.Language != nil {
 		l, err := checkLanguage(*p.Language)
 		if err != nil {
 			writeErr(w, 400, err.Error())
 			return
 		}
 		if l == "" {
 			p.Language = nil
 		} else {
 			p.Language = &l
 		}
 	}
 	if p.BurnAfterReads != nil { // #68: reject negative read budgets
 		if err := parseBurnAfterReads(*p.BurnAfterReads); err != nil {
 			writeErr(w, 400, err.Error())
 			return
 		}
 	}
 	// #40: admin-configurable default expiry
 	if (p.ExpiresIn == nil || *p.ExpiresIn == "") && s.DefaultExpiry != "" {
 		def := s.DefaultExpiry
@@ -209,6 +238,13 @@ func (a *apiServer) handleGetPaste(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if row.PasswordHash.Valid {
 		// #81: every password verification (header, query param, or empty)
 		// goes through the same per-IP+paste unlock limiter as the POST form
 		// path, so brute-force via GET ?password= or X-Paste-Password gets 429.
 		if !rateLimitUnlock(row.ID, r) {
 			writeRateLimited(w, 60)
 			return
 		}
 		// require password via header or query
 		pw := r.Header.Get("X-Paste-Password")
 		if pw == "" {
@@ -293,11 +329,8 @@ func (a *apiServer) handleListMine(w http.ResponseWriter, r *http.Request) {
 		writeJSON(w, 200, map[string]any{"total": 0, "items": []any{}})
 		return
 	}
-	limit, _ := strconv.Atoi(r.URL.Query().Get("limit"))
+	limit := parseLimit(r, 50, 100)
-	if limit <= 0 || limit > 100 {
+	offset := parseOffset(r)
 		limit = 50
 	}
 	offset, _ := strconv.Atoi(r.URL.Query().Get("offset"))
 	rows, total, err := a.store.ListMine(vid, limit, offset)
 	if err != nil {
 		writeErr(w, 500, "db error")
@@ -317,11 +350,8 @@ func (a *apiServer) handleListMine(w http.ResponseWriter, r *http.Request) {
 }
 func (a *apiServer) handleListPublic(w http.ResponseWriter, r *http.Request) {
-	limit, _ := strconv.Atoi(r.URL.Query().Get("limit"))
+	limit := parseLimit(r, 25, 100)
-	if limit <= 0 || limit > 100 {
+	offset := parseOffset(r)
 		limit = 25
 	}
 	offset, _ := strconv.Atoi(r.URL.Query().Get("offset"))
 	rows, total, err := a.store.ListPublic(limit, offset)
 	if err != nil {
 		writeErr(w, 500, "db error")
@@ -0,0 +1,136 @@
 package api
 import (
 	"errors"
 	"fmt"
 	"net/http"
 	"regexp"
 	"strconv"
 	"strings"
 )
 // #68 input-validation helpers. Paste/can payloads are size-capped and list
 // endpoints get a single place where limit/offset are parsed and clamped.
 // maxRequestBody returns the HTTP body cap for JSON create endpoints: the
 // admin-tunable content cap plus headroom for JSON field overhead, floored
 // at 64KiB so a tiny admin-configured cap can't break small requests.
 func (a *apiServer) maxRequestBody() int64 {
 	s := a.settings.get()
 	max := s.MaxContentBytes + 4096
 	if max < 64*1024 {
 		max = 64 * 1024
 	}
 	return max
 }
 // limitRequestBody wraps the request body with http.MaxBytesReader so
 // oversized payloads are cut off server-side instead of being fully decoded
 // into memory before the per-field size check runs (#68). A read over the
 // cap surfaces as *http.MaxBytesError, which handlers map to 413.
 func (a *apiServer) limitRequestBody(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Body != nil {
 			r.Body = http.MaxBytesReader(w, r.Body, a.maxRequestBody())
 		}
 		next.ServeHTTP(w, r)
 	})
 }
 // writeBodyTooLarge emits the 413 response for a body rejected by
 // MaxBytesReader.
 func writeBodyTooLarge(w http.ResponseWriter) {
 	writeErr(w, http.StatusRequestEntityTooLarge, "request body too large")
 }
 // isBodyTooLarge reports whether err came from http.MaxBytesReader.
 func isBodyTooLarge(err error) bool {
 	var mbe *http.MaxBytesError
 	return errors.As(err, &mbe)
 }
 // checkContent validates paste content: rejects whitespace-only content
 // (400) and content over the byte cap (413). Returns (0, "") when valid.
 func checkContent(content string, maxBytes int64) (int, string) {
 	if strings.TrimSpace(content) == "" {
 		return http.StatusBadRequest, "content is required"
 	}
 	if int64(len(content)) > maxBytes { // #40/#68: admin-tunable cap
 		return http.StatusRequestEntityTooLarge,
 			fmt.Sprintf("content exceeds max %d bytes", maxBytes)
 	}
 	return 0, ""
 }
 // parseLimit clamps the ?limit query param: missing/non-numeric/zero/negative
 // or over-max values fall back to def. Zero intentionally maps to the default
 // page size, matching the pre-existing `<= 0` clamp (#68).
 func parseLimit(r *http.Request, def, max int) int {
 	n, err := strconv.Atoi(r.URL.Query().Get("limit"))
 	if err != nil || n <= 0 || n > max {
 		return def
 	}
 	return n
 }
 // parseOffset clamps the ?offset query param: missing/non-numeric or negative
 // values become 0 (#68: negative offsets previously passed through to SQL).
 func parseOffset(r *http.Request) int {
 	n, err := strconv.Atoi(r.URL.Query().Get("offset"))
 	if err != nil || n < 0 {
 		return 0
 	}
 	return n
 }
 // parseBurnAfterReads validates the burn_after_reads field (#68): negative
 // values are rejected; zero/absent mean the default single read.
 func parseBurnAfterReads(n int) error {
 	if n < 0 {
 		return errors.New("burn_after_reads must be a positive number")
 	}
 	return nil
 }
 // #86: bounds for free-form metadata fields on create.
 const (
 	maxTitleLen    = 200
 	maxLanguageLen = 40
 )
 // languageRe restricts language to identifiers like go, c#, f#, c++, objc.
 var languageRe = regexp.MustCompile(`^[a-zA-Z0-9+#-]{1,40}$`)
 // checkTitle validates the paste title (#86): over-max titles are truncated
 // to 200 characters so a bloated listing entry can't be stored; whitespace
 // is trimmed first.
 func checkTitle(title string) (string, error) {
 	title = strings.TrimSpace(title)
 	if len(title) > maxTitleLen {
 		return truncateRunes(title, maxTitleLen), nil
 	}
 	return title, nil
 }
 // checkLanguage validates the language field (#86): optional, max 40 chars,
 // and must match ^[a-zA-Z0-9+#-]{1,40}$. Returns "" for absent/blank values.
 // Anything else malformed is a 400.
 func checkLanguage(lang string) (string, error) {
 	lang = strings.TrimSpace(lang)
 	if lang == "" {
 		return "", nil
 	}
 	if len(lang) > maxLanguageLen || !languageRe.MatchString(lang) {
 		return "", fmt.Errorf("language must match ^[a-zA-Z0-9+#-]{1,40}$ (max %d chars)", maxLanguageLen)
 	}
 	return lang, nil
 }
 // truncateRunes cuts s to at most max runes, keeping the prefix intact.
 func truncateRunes(s string, max int) string {
 	runes := []rune(s)
 	if len(runes) <= max {
 		return s
 	}
 	return string(runes[:max])
 }
@@ -0,0 +1,46 @@
 package web
 import (
 	"net/http"
 	"net/http/httptest"
 	"testing"
 )
 // #59: SecurityHeaders must add the CSP and hardening headers to rendered
 // HTML responses only; JSON and /raw responses pass through untouched.
 func TestSecurityHeaders(t *testing.T) {
 	pages := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "text/html; charset=utf-8")
 		w.Write([]byte("<html><body>ok</body></html>"))
 	})
 	h := SecurityHeaders(pages)
 	rec := httptest.NewRecorder()
 	h.ServeHTTP(rec, httptest.NewRequest("GET", "/", nil))
 	wantCSP := "default-src 'self'; script-src 'self' 'unsafe-inline'; frame-ancestors 'none'"
 	if got := rec.Header().Get("Content-Security-Policy"); got != wantCSP {
 		t.Errorf("CSP = %q, want %q", got, wantCSP)
 	}
 	if got := rec.Header().Get("Referrer-Policy"); got != "no-referrer" {
 		t.Errorf("Referrer-Policy = %q, want no-referrer", got)
 	}
 	if got := rec.Header().Get("X-Content-Type-Options"); got != "nosniff" {
 		t.Errorf("X-Content-Type-Options = %q, want nosniff", got)
 	}
 	// JSON/raw responses: headers are now set unconditionally BEFORE the handler
 	// runs. The previous post-handler approach was silently dropped once a page
 	// handler flushed its template output (headers must be set before WriteHeader).
 	// CSP/nosniff/referrer on non-HTML bodies is harmless and desirable.
 	jsonh := SecurityHeaders(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
 		w.Write([]byte(`{"ok":true}`))
 	}))
 	rec = httptest.NewRecorder()
 	jsonh.ServeHTTP(rec, httptest.NewRequest("GET", "/api/x", nil))
 	if got := rec.Header().Get("Content-Security-Policy"); got != wantCSP {
 		t.Errorf("CSP missing on JSON response: got %q", got)
 	}
 	if got := rec.Header().Get("Referrer-Policy"); got != "no-referrer" {
 		t.Errorf("Referrer-Policy missing on JSON response: got %q", got)
 	}
 }
@@ -63,7 +63,7 @@ const PaletteTable = (() => {
        const filtered = state.filter.length > 0;
        const off = (state.page - 1) * opts.perPage;
        const url = (filtered || state.sortKey)
-          ? opts.endpoint + '?limit=500&offset=0'
+          ? opts.endpoint + '?limit=' + (opts.fetchLimit || 100) + '&offset=0'
          : opts.endpoint + '?limit=' + opts.perPage + '&offset=' + off;
        const res = await fetch(url);
        const data = await res.json();
@@ -328,3 +328,25 @@ func (h *Handlers) HandleAdminPage(w http.ResponseWriter, r *http.Request) {
 // Handlers builds a web.Handlers bound to this UI.
 func (u *UI) Handlers() *Handlers { return &Handlers{UI: u} }
 // #59: security headers for rendered HTML pages. Applied wherever the
 // response is text/html (page templates and the inline can page); JSON API
 // responses and /raw content pass through untouched. script-src allows
 // 'unsafe-inline' because the page templates carry inline scripts; CSP
 // default-src 'self' still blocks external content and object/frame embeds,
 // and frame-ancestors 'none' closes the clickjacking gap flagged in the #34
 // pentest. Runs after the handler so the Content-Type is already set.
 func SecurityHeaders(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		// Set before the handler runs: once a handler writes (template render
 		// flushes), header mutations are silently dropped. Setting the headers
 		// unconditionally is safe: CSP/nosniff/referrer on JSON or /raw bodies
 		// is harmless and arguably desirable.
 		h := w.Header()
 		h.Set("Content-Security-Policy",
 			"default-src 'self'; script-src 'self' 'unsafe-inline'; frame-ancestors 'none'")
 		h.Set("Referrer-Policy", "no-referrer")
 		h.Set("X-Content-Type-Options", "nosniff")
 		next.ServeHTTP(w, r)
 	})
 }