fix(#1455): resolve project-code-prefixed roadmap headings

* fix: remove hardcoded phase project-code prefix cap

Centralize project-code prefix stripping/matching and replace fixed {1,6} caps so long codes (for example MANIFOLD-117) resolve across phase, roadmap parser, roadmap upgrade, and validate flows.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: address review feedback on prefix parsing

- allow project_code prefixes with digits and underscores while preserving milestone parsing
- use shared optional project-code prefix source in phase dir parsing
- extend regression coverage for APP1/APP_1 prefixed phases

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* chore: resolve review nit in phase-id test comment

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: resolve project-code-prefixed roadmap headings

Make getRoadmapPhaseInternal recover from drifted project-code-prefixed ROADMAP headings while preserving canonical bare-heading preference. Add init.phase-op and parser regressions for #1455 and guard gsd-roadmapper against emitting project_code in headings.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* chore: add changeset for project-code phase fix

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* chore: update roadmapper agent size baseline

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix(#1455): tighten project-code prefix regex to [A-Z] start; add boundary test; document source order

Resolves blockers from review:
- Regex changed from [A-Z_][A-Z0-9_]* to [A-Z][A-Z0-9_]* so leading
  underscores (_FOO-7, _-7) are never misread as project-code prefixes;
  adds boundary test asserting both do NOT strip.
- Adds comment to roadmapPhaseLookupSources explaining why 3 sources are
  needed (order-dependent canonical-heading preference).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Solvely-Colin <211764741+Solvely-Colin@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

src/phase.cts

@@ -29,7 +29,14 @@ import coreUtilsMod = require('./core-utils.cjs');
 const { toPosixPath, generateSlugInternal, readSubdirectories } = coreUtilsMod;
 // eslint-disable-next-line @typescript-eslint/no-require-imports -- phase-id.cjs is an export= CommonJS module
 import phaseIdMod = require('./phase-id.cjs');
-const { escapeRegex, normalizePhaseName, phaseMarkdownRegexSource, comparePhaseNum, phaseTokenMatches } = phaseIdMod;
+const {
+  escapeRegex,
+  normalizePhaseName,
+  phaseMarkdownRegexSource,
+  comparePhaseNum,
+  phaseTokenMatches,
+  OPTIONAL_PROJECT_CODE_PREFIX_SOURCE,
+} = phaseIdMod;
 // eslint-disable-next-line @typescript-eslint/no-require-imports -- phase-locator.cjs is an export= CommonJS module
 import phaseLocatorMod = require('./phase-locator.cjs');
 const { findPhaseInternal, getArchivedPhaseDirs } = phaseLocatorMod;
@@ -194,7 +201,7 @@ function cmdPhaseNextDecimal(cwd: string, basePhase: string, raw: boolean): void
       const dirs = entries.filter((e) => e.isDirectory()).map((e) => e.name);
       baseExists = dirs.some((d) => phaseTokenMatches(d, normalized));
 
-      const dirPattern = new RegExp(`^(?:[A-Z]{1,6}-)?${escapeRegex(normalized)}\\.(\\d+)`);
+      const dirPattern = new RegExp(`^${OPTIONAL_PROJECT_CODE_PREFIX_SOURCE}${escapeRegex(normalized)}\\.(\\d+)`);
       for (const dir of dirs) {
         const match = dir.match(dirPattern);
         if (match) decimalSet.add(parseInt(match[1], 10));
@@ -360,7 +367,7 @@ function cmdFindPhase(cwd: string, phase: string, raw: boolean): void {
       if (!match) continue;
 
       const dirMatch =
-        match.match(/^(?:[A-Z]{1,6}-)(\d+[A-Z]?(?:\.\d+)*)-?(.*)/i) ||
+        match.match(new RegExp(`^${OPTIONAL_PROJECT_CODE_PREFIX_SOURCE}(\\d+[A-Z]?(?:\\.\\d+)*)-?(.*)`, 'i')) ||
         match.match(/^(\d+[A-Z]?(?:\.\d+)*)-?(.*)/i);
       const phaseNumber = dirMatch ? dirMatch[1] : normalized;
       const phaseName = dirMatch && dirMatch[2] ? dirMatch[2] : null;
@@ -908,7 +915,7 @@ function cmdPhaseInsert(cwd: string, afterPhase: string, description: string, ra
       const entries = fs.readdirSync(phasesDir, { withFileTypes: true });
       const dirs = entries.filter((e) => e.isDirectory()).map((e) => e.name);
       const decimalPattern = new RegExp(
-        `^(?:[A-Z]{1,6}-)?${escapeRegex(normalizedBase)}\\.(\\d+)`,
+        `^${OPTIONAL_PROJECT_CODE_PREFIX_SOURCE}${escapeRegex(normalizedBase)}\\.(\\d+)`,
       );
       for (const dir of dirs) {
         const dm = dir.match(decimalPattern);