fix(gate): the plan-code guard catches decision codes, and the purge takes them

A plan's decision ids (`D1`, `D4`, `D6-A`) cited in 11 comments and test titles named a document
no reader of this repo has, and the guard had no pattern for them. It has now (mirrored in
audit_metrics), with cases for each form the citations took and for the look-alikes it must leave
alone (a JPEG marker, "3D"); the 11 lines say their why without the id. Case test seen red without
the pattern, the scan red on a planted `D9:`.

frontend/src/components/PlexBrowse.tsx

@@ -68,7 +68,7 @@ const PlexCollectionView = lazy(() => import("./PlexCollectionView"));
 
 const PAGE = 40;
 
-// D3: the "last watched" sort auto-applied when you enter the in-progress watch-state view (most
+// The "last watched" sort auto-applied when you enter the in-progress watch-state view (most
 // recently watched first). Frozen for the same reason as PLEX_SORT_FALLBACK (handed out by reference).
 const LASTWATCHED_SORT: NonNullable<SortState> = Object.freeze({
   key: "lastwatched",
@@ -229,7 +229,7 @@ export default function PlexBrowse() {
     return () => window.removeEventListener("keydown", onKey);
   }, [sub, canStepBack]);
 
-  // D3: entering the in-progress watch-state view auto-applies the "last watched" sort (most recently
+  // Entering the in-progress watch-state view auto-applies the "last watched" sort (most recently
   // watched first); leaving restores the sort that was active before entering. Only the ENTER edge
   // forces the sort, so a manual sort change while in the in-progress view still wins — it's just not
   // carried back out (exit returns to the pre-entry preference). We stash the raw provider `sort`, not

frontend/src/components/PlexDiscover.dom.test.tsx

@@ -273,7 +273,7 @@ describe("PlexDiscover", () => {
 });
 
 // Every rail and the genre grid are lists the keyboard walks (lib/listNav), so `j` goes on
-// from one to the next in page order (owner decision D4).
+// from one to the next in page order (the owner's call).
 describe("PlexDiscover · keyboard", () => {
   it("registers every rail and the genre grid, and j walks on from rail to rail", async () => {
     plexDiscover.mockResolvedValue(fullPayload);

frontend/src/components/ShareDialog.tsx

@@ -235,7 +235,7 @@ function LinkShare({ job }: { job: DownloadJob }) {
     queryFn: () => api.downloadLinks(job.id),
   });
   const [creating, setCreating] = useState(false);
-  // D1: downloadable by default — matches the one-click Share (which relies on the backend
+  // Downloadable by default — matches the one-click Share (which relies on the backend
   // default) and the common "let them have the file" intent. The owner can uncheck it here.
   const [allowDownload, setAllowDownload] = useState(true);
   const [expiryDays, setExpiryDays] = useState<number | null>(null);
@@ -260,7 +260,7 @@ function LinkShare({ job }: { job: DownloadJob }) {
   });
 
   // Open with a link already generated: sharing is almost always the goal, so mint a default
-  // (no password, no expiry, downloadable per D1) link the moment the dialog finds none — as if the
+  // (no password, no expiry, downloadable) link the moment the dialog finds none — as if the
   // user had pressed "New link" → "Create". All further controls (password, download toggle, expiry,
   // extra links, revoke) stay available on the created link and via the "New link" button.
   const autoTried = useRef(false);

frontend/src/components/UpNextCard.tsx

@@ -10,7 +10,7 @@ import { Button } from "./ui/Button";
 import { IconButton } from "./ui/IconButton";
 
 // Up-next / end-card. Shown at episode end when a next item exists and the pref is on, INSTEAD
-// of the old instant jump — so binge stays under the viewer's control (D6-A). Counts down ~10s then
+// of the old instant jump — so binge stays under the viewer's control. Counts down ~10s then
 // advances; "Play now" advances immediately; Cancel/✕ dismisses and stays on the finished frame. It only
 // lives on the play-to-the-end path; credits-auto-skip advances earlier and never reaches this card.
 const COUNTDOWN_S = 10;

frontend/src/components/plexCards.dom.test.tsx

@@ -258,7 +258,7 @@ describe("EpisodeCard a11y", () => {
 });
 
 // In a keyboard-walkable grid or rail the WHOLE card is the item (the ring goes round the
-// poster and its title, D2) and the poster — the card's own role=button — is what Enter opens.
+// poster and its title) and the poster — the card's own role=button — is what Enter opens.
 describe("Plex cards in a keyboard-walkable list", () => {
   const cases = [
     [

frontend/src/lib/keymap.sequence.test.ts

@@ -87,7 +87,7 @@ describe("two-step sequences", () => {
     expect(calls).toEqual(["goDownloads"]);
   });
 
-  // No second step needs a modifier (D1), so a chord with one is the reader changing their mind: it
+  // No second step needs a modifier (see the page-level rows below), so a chord with one is the reader changing their mind: it
   // must reach its own row. Swallowed, `g` then Ctrl+K opened the browser's search, not the palette.
   it("lets a modifier chord abandon the sequence and match as itself", () => {
     const calls: string[] = [];
@@ -148,7 +148,7 @@ describe("page-level scopes under a layer", () => {
 });
 
 describe("the page-level rows", () => {
-  // Owner rule D1, enforced rather than commented: on the Hungarian layout the owner types on, a
+  // The owner's rule, enforced rather than commented: on the Hungarian layout the owner types on, a
   // chord with a modifier (or `/`, `?`, which ARE Shift chords there) is not a quick key.
   it("need no modifier and no Shift-only character", () => {
     for (const s of SHORTCUTS) {

frontend/src/lib/planCodes.contract.test.ts

@@ -24,10 +24,10 @@ const ALLOWED = new Set([
 // Anything else that looks like a code is one — `"""E30:`, `it("E36:`, `# S6:` and `S3's` included.
 const NOT_CODES = /\bS\d{1,2} ?·? ?E\d+|\btitle[=:] ?"[ES]\d{1,2}"|\bE4\/E7\/E9\b/g;
 const PLAN_CODES = [
-  // an epic (`E28`, `E9.5`, `E28/E30`), an older roadmap item (`R14`), a sprint (`S6`, `S3e2`) or a
-  // phase (`P1`) — not `E2E`, not a ruff rule (`S110`), not `S3h`, the media-card decision
-  // docs/DESIGN.md is headed by
-  /\b(?:E\d{1,2}(?:\.\d+)?|R\d{1,2}|S(?!3h\b)\d{1,2}(?:[a-z]\d?)?|P\d)\b/,
+  // an epic (`E28`, `E9.5`, `E28/E30`), an older roadmap item (`R14`), a sprint (`S6`, `S3e2`), a
+  // phase (`P1`) or a plan's decision (`D1`, `D6-A`) — not `E2E`, not a ruff rule (`S110`), not
+  // `S3h`, the media-card decision docs/DESIGN.md is headed by
+  /\b(?:E\d{1,2}(?:\.\d+)?|R\d{1,2}|S(?!3h\b)\d{1,2}(?:[a-z]\d?)?|P\d|D\d{1,2})\b/,
   // a review round (`round 4`, `deep-review`)
   /\b[Rr]ound[ -]\d|deep-review/,
 ];
@@ -58,6 +58,9 @@ describe("plan codes", () => {
       '"""E30: the new sink.',
       'it("E36: keeps x", () => {',
       "// both sides (E28/E30)",
+      "# D1: a newly shared download is downloadable by default",
+      "// binge stays under the viewer's control (D6-A)",
+      "// (owner decision D4)",
       "# the roadmap's R6/R7 pair",
       "// held since E9.5",
       "// (S6) moved it",
@@ -79,6 +82,8 @@ describe("plan codes", () => {
       'expect(btn.textContent).toContain("S2 · E1");',
       "// the S3h media card",
       '"S110", "S112",',
+      "# the JPEG SOI marker (0xFF 0xD8 0xFF)",
+      "// a 3D view",
     ];
     expect(cited.filter((l) => !isPlanCode(l))).toEqual([]);
     expect(clean.filter(isPlanCode)).toEqual([]);