fix(gate): the plan-code guard catches bare sprint and phase codes, and the purge takes the P ones

The sprint alternative matched only `(S6)` or `S3e2`, so the commonest purged form (`# S6:`,
`S3's`, `"""S6 —`, `S1 justified`) and every phase code (`P1`) would come back unflagged; the phase
codes had in fact survived the purge in 16 lines (Plex client sections, the upload's header shape),
now reworded around them.

One pattern now covers epic, roadmap, sprint and phase codes; the named exceptions are TV episode
notation, a fixture's season or episode title (`title="S1"`) and ruff's `E4/E7/E9`, and a ruff rule
like `S110` does not match. The case test lists the purged forms and no longer claims every form.
audit_metrics copies the definition (ASCII, as JavaScript's \b is) and reports it as
plan_code_lines / plan_code_files.

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

@@ -19,17 +19,17 @@ const ALLOWED = new Set([
   "frontend/src/lib/planCodes.contract.test.ts",
   "scripts/audit_metrics.py",
 ]);
-// Named exceptions, cut from a line before it is matched: a test show's episode titled "E1" (the
-// whole string, quotes included) and ruff's default rule families. Anything else that looks like a
-// code is one — a docstring or a test title opening with `"""E30:` / `it("E36:` included.
-const NOT_CODES = /"E\d{1,2}"|\bE4\/E7\/E9\b/g;
+// Named exceptions, cut from a line before it is matched: TV episode notation (`S2 · E5`), a test
+// fixture's season or episode title (`title="S1"`, `title: "E1"`) and ruff's default rule families.
+// 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`) or an older roadmap item (`R14`) — not `E2E`, not a TV
-  // episode (`S2 · E5`)
-  /(?<!S\d{1,2}\s?·?\s?)\b(?:E\d{1,2}(?:\.\d+)?|R\d{1,2})\b(?!E)/,
-  // a sprint cited on its own (`(S6)`, `S3e2`) or a review round (`round 4`, `deep-review`) — not
-  // `S3h`, the media-card decision docs/DESIGN.md is headed by and the design lab labels
-  /\(S\d{1,2}[a-z]?\d?\)|\bS(?!3h\b)\d{1,2}[a-z]\d?\b|\b[Rr]ound[ -]\d|deep-review/,
+  // 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/,
+  // a review round (`round 4`, `deep-review`)
+  /\b[Rr]ound[ -]\d|deep-review/,
 ];
 
 const isPlanCode = (line: string) => {
@@ -53,7 +53,7 @@ function tracked(): string[] {
 }
 
 describe("plan codes", () => {
-  it("are recognised in every form a citation takes", () => {
+  it("are recognised in each form the purged citations took", () => {
     const cited = [
       '"""E30: the new sink.',
       'it("E36: keeps x", () => {',
@@ -61,14 +61,24 @@ describe("plan codes", () => {
       "# the roadmap's R6/R7 pair",
       "// held since E9.5",
       "// (S6) moved it",
+      "# S6: attach the acting user's cookie",
+      '"""S6 — per-user cookies',
+      "// S3's canonical upsert",
+      "// S1 justified that",
+      "// the order since P1",
+      '"""P1\'s invariant',
+      "// a sprint then a roadmap item: S2 R14",
       "// deep-review round 4 found it",
     ];
     const clean = [
       'title="E1",',
+      'title: "S1",',
       "# ruff's default rule set (E4/E7/E9 + F)",
       "// an E2E run",
       "// S2 · E5 is the second episode",
+      'expect(btn.textContent).toContain("S2 · E1");',
       "// the S3h media card",
+      '"S110", "S112",',
     ];
     expect(cited.filter((l) => !isPlanCode(l))).toEqual([]);
     expect(clean.filter(isPlanCode)).toEqual([]);