docs: secure-coding rules for agents, and refresh stale AGENTS.md top-matter (#16)

Two doc commits: a new secure-coding rules section, plus a fix for top-matter the rebrand left stale.

## `9156525` — secure-coding rules

`AGENTS.md` carried two security invariants (bearer auth, CORS) but nothing about the code an agent actually writes here. That is the gap worth closing: measured rates for AI-generated web/backend code are ~40% vulnerable (Pearce et al.), 45% failing security tests (Veracode 2025), and users *with* assistants shipped SQLi at 36% vs 7% for the control group (Perry et al., Stanford). The failure classes cluster on broken access control, injection, session/error handling and invented dependencies — all live surfaces in this repo.

Rules were **extracted, not pasted**. Every one names a guard that already exists in-tree, so the instruction is *match this*, not *invent something*:

| Rule | Existing anchor |
| --- | --- |
| parameterized SQL only; constants may concatenate | `store.go` — all queries use `?` |
| `html/template` only; no `template.HTML` on stored data | `web.go:85` |
| client-supplied URLs pass the fetch gate | `poller.go:144 fetchableSeriesURL` |
| cap remote bodies | `fetch.go:16 maxBodyBytes` |
| `subtle.ConstantTimeCompare`, never `==` | `middleware.go:22`, `session.go:61` |
| generic error out, detail to log, never log the token | `web.go:151` |
| `X-Forwarded-Proto` for Secure; **rightmost** XFF for IP | `session.go:68,101` |
| cookie flags; expiry checked before signature | `session.go:72-94`, `Verify` |
| validate at handler boundary | `handlers.go:48` `MaxBytesReader` 64 KB, 400 on bad key/status/kind |
| site strings via `el({text})`, never `{html}` | `el()` in both userscripts |
| `fetch()`/`authHeaders()` → `API_BASE` only | existing `authHeaders` |
| `localStorage` = cache/queue, never credentials | shared with site JS |

Plus a dependency rule (stdlib first; verify a package exists before adding — ~20% of LLM-proposed packages don't resolve, which is the slopsquatting vector) and a review gate marking auth/CORS/session/crypto/fetch-gate as security-critical.

Deliberately **excluded**: container signing, k8s admission control, IaC scanning, PII/HIPAA/PCI, C/C++ memory safety. Per OpenSSF's guide for AI assistant instructions, irrelevant rules make a model generate code compensating for attacks that cannot happen. None of those apply to a single-user Go + SQLite + userscript stack.

Sources: OWASP AISVS 1.0 Appendix C, OWASP Top 10 / ASVS v5, OpenSSF *Security-Focused Guide for AI Code Assistant Instructions* (2025-08-01).

## `5d4d890` — stale top-matter

The rebrand rewrote root `AGENTS.md` as a compression pass and switched Bromite -> Violentmonkey, but left the project described as a manga-only tracker over two sites. Six sites, two libraries and two userscripts now exist.

Root `AGENTS.md`:

- *What this is* names both scripts with their site lists, the `kind` column, and the `<site>:<series_id>` key shape.
- Origins constraint generalised past Asura/Demonic.
- Records that **kagane and novelfull are reliably Cloudflare-challenged** and browser-polled over CDP. Without it that bullet list reads as contradicting the code, since the paragraph above asserts blocking is "not universal — and not reliably reproducible".
- Diagram says two userscripts.

`backend/AGENTS.md` — two instances of the same defect, found while verifying the above:

- Store key list gained `novelfull|lightnovelworld` and the `kind` column.
- **`NOVEL_USERSCRIPT_PATH` documented** — it shipped in `main.go:150` undocumented.

The dated Cloudflare paragraph is left verbatim: it is a timestamped observation ("Verified 2026-07-26"), so rewriting it would falsify a record rather than update it. `userscript/AGENTS.md` is untouched; it already documents both novel adapters and the `LIBRARY`/`STORE_PREFIX` split.

## Verification

Docs-only, no code touched. Every code reference above was read at `4229c17` before being cited — the fetch gate, body cap, constant-time compares, cookie flags, handler validation, `el()` helper and both route registrations. No invented line numbers.

## Not addressed here

The `API_TOKEN` literal is committed in plaintext in both userscripts and in their `@downloadURL`/`@updateURL` lines. The new rules say not to propagate it, but the actual remedy is rotation plus build-time substitution, since the value is already in git history. Separate change; flagging it so it does not get lost.

Reviewed-on: #16
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

AGENTS.md

@@ -4,21 +4,27 @@ Guidance for OpenCode (and Claude Code) working in this repo.
 
 ## What this is
 
-Manga read-progress tracker, user read on **asurascans.com** (current domain; asuracomic.net 301s here) and **demonicscans.org** via **Violentmonkey**. Userscript inject on-page UI (floating button + slide-in panel), sync progress to self-hosted Go backend so bookmarks unify across both sites and devices.
+Read-progress tracker for two libraries — manga and novels — behind one self-hosted Go backend. Two separate Violentmonkey userscripts inject on-page UI (floating button + slide-in panel) and sync progress, so bookmarks unify across sites and devices:
+
+- `manga-bookmark.user.js` — **asurascans.com** (current domain; asuracomic.net 301s here), **demonicscans.org**, **comix.to**, **kagane.to**.
+- `novel-bookmark.user.js` — **novelfull.com**, **lightnovelworld.net**.
+
+One backend, one `bookmarks` table: a `kind` column (`manga`|`novel`) splits the libraries and the web UI switches between them. Rows are keyed `<site>:<series_id>`.
 
 ## Hard constraints (drive design — don't violate)
 
 Userscript targets **Violentmonkey**, so `GM_*` APIs available, but stay GM-free where plain web APIs suffice — keeps portability across engines:
 - **Avoid `GM_*` unless needed.** Prefer page `localStorage` over `GM_setValue`/`GM_getValue`, on-page UI over `GM_registerMenuCommand`, plain `fetch()` over `GM_xmlhttpRequest` for cross-origin.
 - Cross-origin `fetch()` work **only** against CORS-enabled backend. Manga sites `https://`, so backend **must be HTTPS** (else mixed-content block).
-- Asura and Demonic are **separate origins with separate `localStorage`** — shared remote store only way to unify bookmarks. Cloud sync required, not optional.
+- Every site is its **own origin with its own `localStorage`** — a shared remote store is the only way to unify bookmarks. Cloud sync required, not optional.
 - Userscript run in **isolated world**, so embedded API token safe from site's JS.
 - Cloudflare's block on manga sites **IP-reputation-based, not universal — and not reliably reproducible.** Verified 2026-07-26: plain `curl` from both CGNAT dev machine *and* deployed VPS got clean 200s with real HTML on both asurascans.com and demonicscans.org (homepage, series, chapter pages) — no interactive Turnstile challenge from either IP at test time. Contradicts earlier untested assumption CGNAT dev IP blocked; wasn't, at least this date. Treat "does curl work right now" as live, time-varying fact to re-check, not fixed property of machine — Cloudflare's bot scoring can flip previously-clean IP without notice. Backend fetcher still needs graceful-degrade path for when challenged, and adapters should be **verified against live pages** (Playwright MCP, on-device devtools, direct probe) before finalizing, not assumed from single earlier test.
+- **kagane.to and novelfull.com are the exception to the above** — both sit behind a Cloudflare JavaScript challenge no TLS fingerprint clears, so the backend polls them over CDP (`BROWSER_WS_URL`) and skips them entirely when that's unset. The four other sites poll fine over plain TLS.
 
 ## Architecture
 
 ```
-Violentmonkey userscript (isolated world, per-site adapters, localStorage cache)
+Two Violentmonkey userscripts (isolated world, per-site adapters, localStorage cache)
    -- fetch() HTTPS -->  reverse proxy (TLS + CORS)  -->  Go net/http  -->  SQLite (volume)
 ```
 
@@ -62,9 +68,41 @@ instantly.
 
 ## Security invariants
 
+Existing guarantees — don't regress:
+
 - Auth on `/bookmarks*`: require `Authorization: Bearer <API_TOKEN>`, **constant-time compare**, 401 otherwise.
 - CORS: reflect `Origin` only when in `ALLOWED_ORIGINS`; allow `GET,PUT,DELETE,OPTIONS` + headers `Authorization,Content-Type`; answer preflight `OPTIONS` with `204`.
 
+## Secure coding rules (code you write here)
+
+Anchored to OWASP Top 10 / ASVS. Every rule below already has a working example in-tree — match it, don't start a second convention. AI-written backends fail on exactly these: broken access control, injection, weak session/error handling, invented dependencies.
+
+Go backend:
+
+- SQL always parameterized (`?`). Only compile-time constants (`bookmarkColumns`) may be concatenated into query text — never a request value, not even a validated one.
+- `html/template` only for anything a browser parses, never `text/template`. Never wrap stored or fetched strings in `template.HTML`/`JS`/`URL`; that switches off the escaping every template depends on.
+- Any outbound fetch of a client-supplied URL passes `fetchableSeriesURL` (site + `https` + host check) first. `series_url` arrives in a PUT body, so without the gate the poller will probe arbitrary hosts from the server's own network position. New fetch path reuses the gate rather than re-deriving one.
+- Cap every remote body with `io.LimitReader` (`maxBodyBytes`). An unbounded read is an OOM handed to whatever is on the other end.
+- Compare secrets with `hmac.Equal` / `subtle.ConstantTimeCompare`, never `==`. Covers API token, web password, session MAC.
+- Errors: generic text to the client (`http.Error(w, "internal error", 500)`), detail to `log.Printf`. Never log `API_TOKEN`, `WEB_PASSWORD`, a session cookie value, or a whole `Authorization` header.
+- Proxy headers are trusted only where they already are: `X-Forwarded-Proto` for the Secure cookie flag, **rightmost** `X-Forwarded-For` for client IP (leftmost is attacker-supplied). Don't read either anywhere else.
+- Session cookies keep `HttpOnly`, `SameSite`, `Secure`-when-HTTPS, and expiry checked before signature.
+- Stdlib crypto only. No hand-rolled hashing, no MD5/SHA-1 anywhere security-bearing.
+- Validate at the handler boundary before storing: body capped by `http.MaxBytesReader` (64 KB), empty `key` and unknown `status`/`kind` rejected with `400`. A bad value that reaches the store becomes every later reader's problem.
+
+Userscript:
+
+- Site-derived and stored strings render via `el(..., {text})` / `textContent`. `{html}` and `innerHTML` are for author-written literal markup only (`TEMPLATE`, `CSS`) — never a title, chapter label, or API response field. The page DOM belongs to a third-party site; treat it as attacker-controlled.
+- Isolated world protects the token from the site's JS. It does not protect anything from an `innerHTML` sink you add yourself.
+- The `API_TOKEN` literal sits in both userscripts and must equal backend `API_TOKEN`. Never copy it into logs, docs, commit messages, issues, or a new file. Rotation touches three places: backend env plus both scripts.
+- `fetch()` targets `API_BASE` only — no dynamic origin, no site-supplied URL. `authHeaders()` goes nowhere but the backend.
+- `localStorage` is shared with the site's own JS: cache and queue live there, credentials never do.
+- Wrap every `localStorage` read/write and `JSON.parse` in try/catch (quota, private mode, corrupt entry), as the existing helpers do.
+
+Dependencies: stdlib first; a new module needs a stated reason. Confirm a package actually exists before adding it — a plausible name may be fiction (~20% of LLM-proposed packages don't resolve, which is how slopsquatting lands). Pin exact versions.
+
+Review gate: auth, CORS, session, crypto, and the fetch gate are security-critical. Editing one is not a drive-by change — say which invariant you preserved and run `go test ./...` before calling it done.
+
 ## Comments
 
 Comment only if code alone can't carry info. Cost per read — must earn spot.

backend/AGENTS.md

@@ -11,7 +11,7 @@ Guidance for OpenCode (and Claude Code) working under `backend/`. See root `AGEN
   packages together into `newRouter`. Root-level `*_test.go` hold
   integration tests that exercise the full router; unit tests for a
   package live beside it under `internal/`.
-- **Single-user store.** One `bookmarks` table keyed `<site>:<series_id>` (`asura`|`demonic`|`comix`|`kagane`). Sync **last-write-wins**. Schema and endpoint list in plan.
+- **Single-user store.** One `bookmarks` table keyed `<site>:<series_id>` (`asura`|`demonic`|`comix`|`kagane`|`novelfull`|`lightnovelworld`), with a `kind` column (`manga`|`novel`) splitting the two libraries. Sync **last-write-wins**. Schema and endpoint list in plan.
 - **Endpoints:** `GET /bookmarks`, `PUT /bookmarks/{key}` (upsert; see `updated_at` rule below), `DELETE /bookmarks/{key}`, `GET /healthz` (no auth).
 - **Web UI:** same binary serve password-gated browser UI on second
   hostname — `GET /` (list, or login page when no session),
@@ -75,8 +75,10 @@ Guidance for OpenCode (and Claude Code) working under `backend/`. See root `AGEN
   (gates browser UI; unset disable it),
   `LATEST_CHAPTER_POLL_ENABLED`/`_COOLDOWN`/`_INTERVAL`/`_BATCH`/`_STAGGER`
   (background latest-chapter poller; defaults on, `1h`/`10m`/`14`/`20s`).
-  `USERSCRIPT_PATH` (file served at `/u/{token}/manga-bookmark.user.js`,
-  default `/userscript/manga-bookmark.user.js`, supplied by bindmount).
+  `USERSCRIPT_PATH` and `NOVEL_USERSCRIPT_PATH` (files served at
+  `/u/{token}/manga-bookmark.user.js` and `/u/{token}/novel-bookmark.user.js`,
+  defaults `/userscript/manga-bookmark.user.js` and
+  `/userscript/novel-bookmark.user.js`, both supplied by bindmount).
   `BROWSER_WS_URL` (headless-shell CDP endpoint for kagane and novelfull;
   unset disables browser polling and leaves those sites to the userscript
   alone).