Close the door the edge gate used to hold

A security review of the whole repo. The queries were already scoped, the
OIDC flow already did state and nonce and PKCE, the session tokens were
already stored as hashes. What it found was mostly the seam between the
code and the deployment — and one place where the deployment quietly
undid the code.

The one that matters: with any AUTHENTIK_* variable missing, Petal fell
back to resolving every request to the single `local` user. That is right
on a laptop and a catastrophe on a public host, and Phase 16 removed the
Traefik basic-auth gate that used to stand behind the mistake. A typo in
the client secret would have served her journals to the open internet and
said so only in a log line nobody reads. It now refuses to start, guarded
by default for any BASE_URL that isn't loopback.

Then the one that would have been fixed and wasn't: stored images now
serve under `default-src 'none'; sandbox`, so an SVG pasted into a
document can't run as a page on Petal's own origin. Traefik's
customresponseheaders *overwrites*, so the CSP declared in the compose
labels would have silently replaced that per-route policy in production.
The whole header block moved into the binary, where a route can tighten
its own and a test can prove it; only HSTS stays at the edge, where TLS
actually terminates.

The rest, smaller:

  - PETAL_ALLOWED_SUBS empty means everyone authentik authenticates, and
    authentik here fronts half a dozen applications. Still legal, now
    said out loud every boot, and set in both env examples.
  - LLM failures relayed err.Error() to the browser, which carries the
    address of the inference box on the far side of the VPN. Logged
    instead; the client only ever rendered "the helper is resting".
  - Exports scheme-check their links. Escaping makes a URL safe to sit
    in an attribute and says nothing about following it, and an export
    is the one artifact here meant to leave. Writing the test found the
    markdown image src, which I'd missed reading it.
  - The draft rescue is namespaced per account and cleared on sign-out.
    Everything else in localStorage is a preference; this is her unsaved
    writing, sitting in a profile two people share.
  - /auth/logout is POST-only. With SameSite=Lax a GET route lets any
    page on the internet sign her out mid-draft.
  - Image uploads get a per-account allowance and the TTS cache a size
    cap. Both share the encrypted volume the database is on, and a full
    disk is SQLite failing to write, not a feature degrading.
  - The session cookie takes the __Host- prefix over https, so nothing
    else under parodia.dev can plant one. Old cookies still resolve;
    nobody is signed out to get there.
  - npm audit: linkify-it and postcss.

Verified: go build, go vet, the full Go suite, tsc, 195 frontend tests,
npm audit clean. The startup guard and both CSPs checked against a
running server rather than only asserted.

Claude-Session: https://claude.ai/code/session_016y6gyuHkQXPiEuW8RGQyua

internal/tts/handler.go

@@ -21,6 +21,7 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
+	"sync/atomic"
 	"time"
 	"unicode/utf8"
 
@@ -97,6 +98,7 @@ type Handler struct {
 	cacheDir string
 	format   audioFormat
 	client   *http.Client
+	writes   atomic.Uint64 // cache writes since boot; drives the prune throttle
 }
 
 // New builds a Handler from config. It returns (nil, false) when TTS_ENDPOINT is
@@ -233,6 +235,7 @@ func (h *Handler) synth(w http.ResponseWriter, r *http.Request) {
 		if err := os.WriteFile(tmp, audio, 0o644); err == nil {
 			_ = os.Rename(tmp, path)
 		}
+		h.pruneCache()
 	}
 
 	w.Header().Set("Content-Type", h.format.contentType)
@@ -240,6 +243,80 @@ func (h *Handler) synth(w http.ResponseWriter, r *http.Request) {
 	_, _ = w.Write(audio)
 }
 
+// maxCacheBytes bounds the whole clip cache at 512 MiB.
+//
+// Each clip is small, so nothing about ordinary reading approaches this — a
+// year of tapping words is tens of megabytes. What it bounds is the shape of
+// the endpoint: the cache key is the *text*, so a client asking for four
+// thousand distinct characters at a time writes a new file every request, for
+// as long as it cares to. That is an authenticated writer filling the same
+// encrypted volume the database lives on, and a full disk is SQLite failing to
+// write, not merely read-aloud getting slower.
+const maxCacheBytes = 512 << 20
+
+// pruneEvery throttles the sweep: checking the directory on every synthesis
+// would stat the whole cache for each new word. Synthesis is already the slow
+// path and misses are rare once a writer settles, so one sweep per this many
+// cache writes keeps the cost invisible while still converging long before the
+// limit means anything.
+const pruneEvery = 64
+
+// pruneCache trims the cache back under maxCacheBytes, oldest-first, and is a
+// no-op the great majority of the time it is called.
+//
+// Oldest by modification time is a fair approximation of least-recently-useful
+// here: a clip is written once and only ever read afterwards, so its age is how
+// long ago someone wanted it. Evicting one costs a re-synthesis, never data —
+// which is why this can be as approximate as it likes, and why every error
+// along the way is simply given up on.
+func (h *Handler) pruneCache() {
+	if n := h.writes.Add(1); n%pruneEvery != 0 {
+		return
+	}
+
+	entries, err := os.ReadDir(h.cacheDir)
+	if err != nil {
+		return
+	}
+	type clip struct {
+		path string
+		size int64
+		mod  time.Time
+	}
+	var clips []clip
+	var total int64
+	for _, e := range entries {
+		if e.IsDir() {
+			continue
+		}
+		info, err := e.Info()
+		if err != nil {
+			continue
+		}
+		clips = append(clips, clip{filepath.Join(h.cacheDir, e.Name()), info.Size(), info.ModTime()})
+		total += info.Size()
+	}
+	if total <= maxCacheBytes {
+		return
+	}
+
+	sort.Slice(clips, func(i, j int) bool { return clips[i].mod.Before(clips[j].mod) })
+	// Drop to 80% rather than exactly to the line, so the next few hundred
+	// clips don't each trigger another sweep.
+	target := int64(maxCacheBytes / 100 * 80)
+	removed := 0
+	for _, c := range clips {
+		if total <= target {
+			break
+		}
+		if os.Remove(c.path) == nil {
+			total -= c.size
+			removed++
+		}
+	}
+	fmt.Fprintf(os.Stderr, "tts: cache over %d bytes — evicted %d oldest clip(s)\n", int64(maxCacheBytes), removed)
+}
+
 // serve streams a cached clip with a long-lived immutable cache header (the URL
 // is content-addressed, so the bytes never change for a given request).
 func (h *Handler) serve(w http.ResponseWriter, r *http.Request, path string) {