Add HTTP service hardening policy for 1.0 releases (#17)

Closes #16

Adds a comprehensive HTTP/web service security hardening policy to `REPO_POLICIES.md` that must be satisfied before tagging 1.0. The policy covers all items sneak specified (without limitation):

**Security headers** — HSTS (min 1 year, includeSubDomains), CSP (restrictive `default-src 'self'` baseline), X-Frame-Options / frame-ancestors, X-Content-Type-Options: nosniff, Referrer-Policy, Permissions-Policy.

**Request/response limits** — max request body size on all endpoints, max response size for paginated APIs, ReadTimeout + ReadHeaderTimeout (slowloris defense), WriteTimeout, IdleTimeout, per-handler execution time limits.

**Authentication & session security** — rate limiting on password-based auth (API keys exempt as high-entropy), CSRF tokens on state-mutating forms (header-auth APIs exempt), bcrypt/scrypt/argon2 for passwords, session cookies with HttpOnly + Secure + SameSite.

**Reverse proxy awareness** — true client IP detection via X-Forwarded-For/X-Real-IP with trusted proxy allowlist (never trust unconditionally).

**CORS** — explicit origin allowlist for authenticated endpoints; wildcard only for public unauthenticated read-only APIs.

**Error handling** — no leaking stack traces, SQL queries, file paths, or implementation details to clients.

**TLS** — HSTS and secure cookie flags required regardless of whether the service terminates TLS directly or sits behind a reverse proxy.

The policy is explicitly non-exhaustive (defense-in-depth: "when in doubt, harden").

Also adds corresponding checklist sections to `EXISTING_REPO_CHECKLIST.md` and `NEW_REPO_CHECKLIST.md` so that HTTP hardening is verified during repo setup and 1.0 preparation.

Co-authored-by: user <user@Mac.lan guest wan>
Co-authored-by: clawbot <clawbot@eeqj.de>
Reviewed-on: #17
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

prompts/EXISTING_REPO_CHECKLIST.md

@@ -1,6 +1,6 @@
 ---
 title: Existing Repo Checklist
-last_modified: 2026-02-22
+last_modified: 2026-03-10
 ---
 
 Use this checklist when beginning work in a repo that may not yet conform to our
@@ -78,6 +78,22 @@ with your task.
       `internal/`, `static/`, etc.)
 - [ ] Go migrations in `internal/db/migrations/` and embedded in binary
 
+# HTTP Service Hardening (if targeting 1.0 and the repo is an HTTP/web service)
+
+- [ ] Security headers set on all responses (HSTS, CSP, X-Frame-Options,
+      X-Content-Type-Options, Referrer-Policy, Permissions-Policy)
+- [ ] Request body size limits enforced on all endpoints
+- [ ] Read/write/idle timeouts configured on the HTTP server (slowloris defense)
+- [ ] Per-handler execution time limits in place
+- [ ] Password-based auth endpoints are rate-limited
+- [ ] CSRF tokens on all state-mutating HTML forms
+- [ ] Passwords hashed with bcrypt, scrypt, or argon2
+- [ ] Session cookies use HttpOnly, Secure, and SameSite attributes
+- [ ] True client IP correctly detected behind reverse proxy (trusted proxy
+      allowlist configured)
+- [ ] CORS restricted to explicit origin allowlist for authenticated endpoints
+- [ ] Error responses do not leak stack traces, SQL queries, or internal paths
+
 # Final
 
 - [ ] `make check` passes

prompts/REPO_POLICIES.md

@@ -92,20 +92,19 @@ style conventions are in separate documents:
 - Never commit secrets. `.env` files, credentials, API keys, and private keys
   must be in `.gitignore`. No exceptions.
 
-- Build artifacts and code-derived data (compiled output, bundled JS, minified
-  CSS, generated code) must NOT be committed to the repository if they can be
-  generated during the build process. The Dockerfile or build system should
-  produce these artifacts at build time. Notable exception: Go
-  protobuf-generated files (`.pb.go`) may be committed because Go module
-  consumers use `go get` which downloads source code but does not execute build
-  steps.
-
 - `.gitignore` should be comprehensive from the start: OS files (`.DS_Store`),
   editor files (`.swp`, `*~`), language build artifacts, and `node_modules/`.
   Fetch the standard `.gitignore` from
   `https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitignore` when setting up
   a new repo.
 
+- **No build artifacts in version control.** Code-derived data (compiled
+  bundles, minified output, generated assets) must never be committed to the
+  repository if it can be avoided. The build process (e.g. Dockerfile, Makefile)
+  should generate these at build time. Notable exception: Go protobuf generated
+  files (`.pb.go`) ARE committed because repos need to work with `go get`, which
+  downloads code but does not execute code generation.
+
 - Never use `git add -A` or `git add .`. Always stage files explicitly by name.
 
 - Never force-push to `main`.
@@ -129,6 +128,66 @@ style conventions are in separate documents:
 - Dockerized web services listen on port 8080 by default, overridable with
   `PORT`.
 
+- **HTTP/web services must be hardened for production internet exposure before
+  tagging 1.0.** This means full compliance with security best practices
+  including, without limitation, all of the following:
+    - **Security headers** on every response:
+        - `Strict-Transport-Security` (HSTS) with `max-age` of at least one year
+          and `includeSubDomains`.
+        - `Content-Security-Policy` (CSP) with a restrictive default policy
+          (`default-src 'self'` as a baseline, tightened per-resource as
+          needed). Never use `unsafe-inline` or `unsafe-eval` unless
+          unavoidable, and document the reason.
+        - `X-Frame-Options: DENY` (or `SAMEORIGIN` if framing is required).
+          Prefer the `frame-ancestors` CSP directive as the primary control.
+        - `X-Content-Type-Options: nosniff`.
+        - `Referrer-Policy: strict-origin-when-cross-origin` (or stricter).
+        - `Permissions-Policy` restricting access to browser features the
+          application does not use (camera, microphone, geolocation, etc.).
+    - **Request and response limits:**
+        - Maximum request body size enforced on all endpoints (e.g. Go
+          `http.MaxBytesReader`). Choose a sane default per-route; never accept
+          unbounded input.
+        - Maximum response body size where applicable (e.g. paginated APIs).
+        - `ReadTimeout` and `ReadHeaderTimeout` on the `http.Server` to defend
+          against slowloris attacks.
+        - `WriteTimeout` on the `http.Server`.
+        - `IdleTimeout` on the `http.Server`.
+        - Per-handler execution time limits via `context.WithTimeout` or
+          chi/stdlib `middleware.Timeout`.
+    - **Authentication and session security:**
+        - Rate limiting on password-based authentication endpoints. API keys are
+          high-entropy and not susceptible to brute force, so they are exempt.
+        - CSRF tokens on all state-mutating HTML forms. API endpoints
+          authenticated via `Authorization` header (Bearer token, API key) are
+          exempt because the browser does not attach these automatically.
+        - Passwords stored using bcrypt, scrypt, or argon2 — never plain-text,
+          MD5, or SHA.
+        - Session cookies set with `HttpOnly`, `Secure`, and `SameSite=Lax` (or
+          `Strict`) attributes.
+    - **Reverse proxy awareness:**
+        - True client IP detection when behind a reverse proxy
+          (`X-Forwarded-For`, `X-Real-IP`). The application must accept
+          forwarded headers only from a configured set of trusted proxy
+          addresses — never trust `X-Forwarded-For` unconditionally.
+    - **CORS:**
+        - Authenticated endpoints must restrict `Access-Control-Allow-Origin` to
+          an explicit allowlist of known origins. Wildcard (`*`) is acceptable
+          only for public, unauthenticated read-only APIs.
+    - **Error handling:**
+        - Internal errors must never leak stack traces, SQL queries, file paths,
+          or other implementation details to the client. Return generic error
+          messages in production; detailed errors only when `DEBUG` is enabled.
+    - **TLS:**
+        - Services never terminate TLS directly. They are always deployed behind
+          a TLS-terminating reverse proxy. The service itself listens on plain
+          HTTP. However, HSTS headers and `Secure` cookie flags must still be
+          set by the application so that the browser enforces HTTPS end-to-end.
+
+    This list is non-exhaustive. Apply defense-in-depth: if a standard security
+    hardening measure exists for HTTP services and is not listed here, it is
+    still expected. When in doubt, harden.
+
 - `README.md` is the primary documentation. Required sections:
     - **Description**: First line must include the project name, purpose,
       category (web server, SPA, CLI tool, etc.), license, and author. Example: