brain-of-reese/.agent/phases/todo/33_cache_busting/02_caching_middleware.md

Task 02 — Caching middleware + wiring + integration tests

Phase: 33_cache_busting · Source: TODO.md:6 — "the pages are too sticky" (HTML revalidation + versioned asset URLs + immutable assets) Story: .agent/user_stories/cache-busting.md

Objective

Apply the caching behavior at the transport layer: HTML pages no-cache with ?v=<token> on every local asset reference; /assets/* immutable 1-year; everything else (all /api/*, including SSE) untouched.

Work

1. app/core/caching.py (extend task 01's module):
   • HTML_PAGES: tuple[str, ...] = ("/", "/index.html", "/sources.html", "/document.html", "/login.html", "/tuning.html").
   • _ASSET_REF_RE = re.compile(r'((?:href|src)="(?:/)?assets/[^"?#]+)(")') — matches <link rel="stylesheet" href="/assets/styles.css">, <script src="assets/markdown.js"></script> (no leading slash!), and <script type="module" src="/assets/app.js">; the rewrite appends ?v=<token> before the closing quote, only when the reference has no query/hash yet (idempotent — never a double ?v=).
   • def rewrite_asset_refs(html: str, token: str) -> str — the pure, unit-testable rewrite.
   • def configure_caching(app: FastAPI) -> None — one @app.middleware("http") (or equivalent Starlette middleware) that, after the response is produced:
     • path.startswith("/assets/") → response.headers["Cache-Control"] = "public, max-age=31536000, immutable" (header only — never touch the body).
     • request.url.path in HTML_PAGES and response content-type is text/html → Cache-Control: no-cache + response.body = rewrite_asset_refs(body, asset_version()) (body via await response.body() — works for the buffered StaticFiles/FileResponse HTML responses; on any error or non-text/html, fall through to the unmodified response with only no-cache).
     • everything else → completely untouched (no header, no body work). The /api/* SSE stream in particular must not be read or rewritten.
2. app/main.py — from app.core.caching import configure_caching; call configure_caching(app) inside create_app() after the routers (order: middleware wraps the whole app — call it before return app).
3. tests/unit/test_caching.py (extend) — rewrite_asset_refs:
   • versioned: href="/assets/styles.css" → href="/assets/styles.css?v=abc123"; src="assets/markdown.js" (no slash) → versioned; src="/assets/app.js" (module script) → versioned.
   • idempotent: an already-?v=-tagged reference is not double-tagged; a #fragment or existing ?query reference is left alone.
   • non-asset references untouched (href="/sources.html", href="data:…", href="/login.html?next=…").
4. tests/integration/test_api.py (extend):
   • GET / → 200, cache-control: no-cache; body contains href="/assets/styles.css?v=<token>" with a non-empty token matching asset_version(); the unversioned string href="/assets/styles.css"> is gone from the body.
   • each of the other four pages (/sources.html, /document.html, /login.html, /tuning.html) → no-cache + at least one versioned asset reference.
   • GET /assets/styles.css → 200, cache-control contains immutable and max-age=31536000.
   • GET /api/health → response has no cache-control injected (baseline: FastAPI's default) — assert equality with the pre-middleware behavior; the SSE chat endpoint (tests/integration/test_chat_api.py) stays green unmodified.
   • the existing no-CDN test (test_html_pages_served_locally_no_cdn) stays green — the rewritten references are still same-origin.
5. tests/unit/test_main.py — app creation still succeeds with the middleware wired (existing creation tests stay green; add an assertion that create_app()'s middleware stack includes the caching middleware by name).

Testing & Quality

• Unit: Work steps 3 + 5; Integration: Work step 4.
• Coverage: >90% on app/core/caching.py; app/ TOTAL ≥ pre-change.

Completion Criteria

• All new unit + integration tests green; the full suite green (especially test_chat_api.py — SSE unaffected).
• Manual check: curl -si localhost:8000/ | grep -i cache-control → no-cache; the HTML body shows ?v=… asset refs; curl -si localhost:8000/assets/styles.css | grep -i cache-control → immutable.
• uv run ruff check . && uv run pyright clean.