fix(#3685): report phase-complete write flags from the transaction, not the filesystem (#3826)

* test(#3685): failing-first regression coverage for phase-complete write flags

`phase complete` reports `roadmap_updated`/`state_updated` from
`fs.existsSync(path)`, so both read `true` whenever the file merely exists —
including when the transaction wrote nothing. Add the regression tests that
prove it, plus the negative-space and true-direction pins, before the fix.

New in tests/phase.test.cjs:
- roadmap_updated is false when the transaction rewrites nothing (FAILS today)
- state_updated is false when the transaction rewrites nothing, and stays
  false on a third consecutive run (FAILS today)
- both flags are true when the transaction genuinely rewrites (pins the true
  direction so the fix cannot be tightened into always-false)
- each flag stays false when its file is absent

The STATE.md cases pin the clock via GSD_TEST_MODE + GSD_NOW_MS
(src/clock.cts:43-70) because syncStateFrontmatter stamps a
millisecond-resolution `last_updated:` on every write, which would otherwise
make the no-op unobservable.

Also strengthens four pre-existing `=== true` assertions on these fields that
passed vacuously: each now pairs the flag assertion with a content-changed
assertion against a pre-call snapshot, so the `true` is earned.

Refs #3685

* fix(#3685): report phase-complete write flags from the transaction, not the filesystem

`phase complete` computed `roadmap_updated` and `state_updated` as
`fs.existsSync(path)`, so both read `true` for any project that had the file at
all — including a run that rewrote nothing. The flags are the only signal a
caller has that the rollup landed, so a no-op was indistinguishable from a
successful write and a stale ROADMAP went unnoticed until something downstream
read wrong numbers.

Both flags now reflect whether that file's content actually changed in the
transaction, computed at the existing `writes.push({filePath, before, after})`
sites — the same contract `requirements_updated` has honored since #2316-3, and
the same correction #2640/#2974 already applied to `phase remove`.

Nothing about what gets written changes; only what gets reported.

Fixes #3685

* chore(changeset): backfill PR number for #3685 fragment

---------

Co-authored-by: sim <sim@local>

src/phase.cts

@@ -2261,6 +2261,12 @@ function cmdPhaseComplete(cwd: string, phaseNum: string, raw: boolean): void {
     ? (phaseInfo['summaries'] as string[]).length
     : 0;
   let requirementsUpdated = false;
+  // #3685: mirror requirementsUpdated's diff-tracking contract at the
+  // writes.push({filePath, before, after}) sites below, rather than
+  // reporting via fs.existsSync (which is true whenever the file merely
+  // exists, not when the transaction actually wrote a change).
+  let roadmapUpdated = false;
+  let stateUpdated = false;
 
   const warnings: string[] = [];
   // ADR-3408 §8.5 / D2 (#3374): "liberal but visible" — when the write-seam
@@ -2680,6 +2686,7 @@ function cmdPhaseComplete(cwd: string, phaseNum: string, raw: boolean): void {
           before: originalRoadmapContent,
           after: roadmapContent,
         });
+        roadmapUpdated = roadmapContent !== originalRoadmapContent;
 
         const reqPath = path.join(planningDir(cwd), 'REQUIREMENTS.md');
         if (fs.existsSync(reqPath)) {
@@ -3253,6 +3260,7 @@ function cmdPhaseComplete(cwd: string, phaseNum: string, raw: boolean): void {
         }
 
         writes.push({ filePath: statePath, before: originalStateContent, after: stateContent });
+        stateUpdated = stateContent !== originalStateContent;
       }
 
       anyPlanningWrite = writePlanningFileSet(writes) > 0;
@@ -3319,8 +3327,8 @@ function cmdPhaseComplete(cwd: string, phaseNum: string, raw: boolean): void {
     next_phase_name: nextPhaseName,
     is_last_phase: isLastPhase,
     date: today,
-    roadmap_updated: fs.existsSync(roadmapPath),
-    state_updated: fs.existsSync(statePath),
+    roadmap_updated: roadmapUpdated,
+    state_updated: stateUpdated,
     requirements_updated: requirementsUpdated,
     auto_pruned: autoPruned,
     warnings,