fix: dispatch plan-slice when task plan files are missing (#909) (#923)

When a slice plan (S03-PLAN.md) was pre-created during roadmapping
but plan-slice never ran to generate per-task files (tasks/T01-PLAN.md),
deriveState returned 'executing' phase. execute-task then failed because
the task plan didn't exist, creating an infinite restart loop.

Fix: In deriveState, when the tasks directory exists but has zero .md
files and the slice plan references tasks, return 'planning' phase
instead of 'executing'. This causes plan-slice to dispatch and generate
the missing task plans.

Tests updated: 6 test files that create synthetic state fixtures now
include a stub task plan file so their 'executing' phase assertions
remain valid.

src/resources/extensions/gsd/state.ts

@@ -26,6 +26,7 @@ import {
   resolveSlicePath,
   resolveSliceFile,
   resolveTaskFile,
+  resolveTasksDir,
   resolveGsdRootFile,
   gsdRoot,
 } from './paths.js';
@@ -34,6 +35,7 @@ import { milestoneIdSort, findMilestoneIds } from './guided-flow.js';
 import { nativeBatchParseGsdFiles, type BatchParsedFile } from './native-parser-bridge.js';
 
 import { join, resolve } from 'path';
+import { existsSync, readdirSync } from 'node:fs';
 import { debugCount, debugTime } from './debug-logger.js';
 
 // ─── Query Functions ───────────────────────────────────────────────────────
@@ -573,6 +575,34 @@ async function _deriveStateImpl(basePath: string): Promise<GSDState> {
     title: activeTaskEntry.title,
   };
 
+  // ── Task plan file check (#909) ──────────────────────────────────────
+  // The slice plan may reference tasks but per-task plan files may be
+  // missing — e.g. when the slice plan was pre-created during roadmapping.
+  // If the tasks dir exists but has literally zero files (empty dir from
+  // mkdir), fall back to planning so plan-slice generates task plans.
+  const tasksDir = resolveTasksDir(basePath, activeMilestone.id, activeSlice.id);
+  if (tasksDir && existsSync(tasksDir) && slicePlan.tasks.length > 0) {
+    const allFiles = readdirSync(tasksDir).filter(f => f.endsWith(".md"));
+    if (allFiles.length === 0) {
+      return {
+        activeMilestone,
+        activeSlice,
+        activeTask: null,
+        phase: 'planning',
+        recentDecisions: [],
+        blockers: [],
+        nextAction: `Task plan files missing for ${activeSlice.id}. Run plan-slice to generate task plans.`,
+        registry,
+        requirements,
+        progress: {
+          milestones: milestoneProgress,
+          slices: sliceProgress,
+          tasks: taskProgress,
+        },
+      };
+    }
+  }
+
   // ── Blocker detection: scan completed task summaries ──────────────────
   // If any completed task has blocker_discovered: true and no REPLAN.md
   // exists yet, transition to replanning-slice instead of executing.

src/resources/extensions/gsd/tests/derive-state-db.test.ts

@@ -103,6 +103,7 @@ async function main(): Promise<void> {
       writeFile(base, 'milestones/M001/M001-ROADMAP.md', ROADMAP_CONTENT);
       writeFile(base, 'milestones/M001/slices/S01/S01-PLAN.md', PLAN_CONTENT);
       writeFile(base, 'milestones/M001/slices/S01/tasks/.gitkeep', '');
+      writeFile(base, 'milestones/M001/slices/S01/tasks/T01-PLAN.md', '# T01 Plan');
       writeFile(base, 'REQUIREMENTS.md', REQUIREMENTS_CONTENT);
 
       // Derive state from files only (no DB)
@@ -166,6 +167,7 @@ async function main(): Promise<void> {
       writeFile(base, 'milestones/M001/M001-ROADMAP.md', ROADMAP_CONTENT);
       writeFile(base, 'milestones/M001/slices/S01/S01-PLAN.md', PLAN_CONTENT);
       writeFile(base, 'milestones/M001/slices/S01/tasks/.gitkeep', '');
+      writeFile(base, 'milestones/M001/slices/S01/tasks/T01-PLAN.md', '# T01 Plan');
 
       // No DB open — isDbAvailable() is false
       assertTrue(!isDbAvailable(), 'fallback: DB is not available');
@@ -189,6 +191,7 @@ async function main(): Promise<void> {
       writeFile(base, 'milestones/M001/M001-ROADMAP.md', ROADMAP_CONTENT);
       writeFile(base, 'milestones/M001/slices/S01/S01-PLAN.md', PLAN_CONTENT);
       writeFile(base, 'milestones/M001/slices/S01/tasks/.gitkeep', '');
+      writeFile(base, 'milestones/M001/slices/S01/tasks/T01-PLAN.md', '# T01 Plan');
 
       // Open DB but insert nothing — empty artifacts table
       openDatabase(':memory:');
@@ -219,6 +222,7 @@ async function main(): Promise<void> {
       writeFile(base, 'milestones/M001/M001-ROADMAP.md', ROADMAP_CONTENT);
       writeFile(base, 'milestones/M001/slices/S01/S01-PLAN.md', PLAN_CONTENT);
       writeFile(base, 'milestones/M001/slices/S01/tasks/.gitkeep', '');
+      writeFile(base, 'milestones/M001/slices/S01/tasks/T01-PLAN.md', '# T01 Plan');
       writeFile(base, 'REQUIREMENTS.md', REQUIREMENTS_CONTENT);
 
       // Open DB but only insert the roadmap — plan and requirements missing from DB
@@ -348,6 +352,7 @@ async function main(): Promise<void> {
       writeFile(base, 'milestones/M001/M001-ROADMAP.md', ROADMAP_CONTENT);
       writeFile(base, 'milestones/M001/slices/S01/S01-PLAN.md', PLAN_CONTENT);
       writeFile(base, 'milestones/M001/slices/S01/tasks/.gitkeep', '');
+      writeFile(base, 'milestones/M001/slices/S01/tasks/T01-PLAN.md', '# T01 Plan');
 
       openDatabase(':memory:');
       insertArtifactRow('milestones/M001/M001-ROADMAP.md', ROADMAP_CONTENT, {

src/resources/extensions/gsd/tests/derive-state-deps.test.ts

@@ -45,6 +45,7 @@ function writeContext(base: string, mid: string, frontmatter: string): void {
 function writeSlicePlan(base: string, mid: string, sid: string, content: string): void {
   const dir = join(base, '.gsd', 'milestones', mid, 'slices', sid);
   mkdirSync(join(dir, 'tasks'), { recursive: true });
+  writeFileSync(join(dir, "tasks", "T01-PLAN.md"), "# T01 Plan\n");
   writeFileSync(join(dir, `${sid}-PLAN.md`), content);
 }
 

src/resources/extensions/gsd/tests/derive-state-draft.test.ts

@@ -45,6 +45,7 @@ function writeRoadmap(base: string, mid: string, content: string): void {
 function writePlan(base: string, mid: string, sid: string, content: string): void {
   const dir = join(base, '.gsd', 'milestones', mid, 'slices', sid);
   mkdirSync(join(dir, 'tasks'), { recursive: true });
+  writeFileSync(join(dir, "tasks", "T01-PLAN.md"), "# T01 Plan\n");
   writeFileSync(join(dir, `${sid}-PLAN.md`), content);
 }
 

src/resources/extensions/gsd/tests/derive-state.test.ts

@@ -22,8 +22,17 @@ function writeRoadmap(base: string, mid: string, content: string): void {
 
 function writePlan(base: string, mid: string, sid: string, content: string): void {
   const dir = join(base, '.gsd', 'milestones', mid, 'slices', sid);
-  mkdirSync(join(dir, 'tasks'), { recursive: true });
+  const tasksDir = join(dir, 'tasks');
+  mkdirSync(tasksDir, { recursive: true });
   writeFileSync(join(dir, `${sid}-PLAN.md`), content);
+  // Create stub task plan files for any tasks in the plan content (#909)
+  // so deriveState doesn't fall back to planning phase.
+  const taskMatches = content.matchAll(/\*\*(T\d+):/g);
+  for (const m of taskMatches) {
+    const tid = m[1];
+    const planPath = join(tasksDir, `${tid}-PLAN.md`);
+    writeFileSync(planPath, `# ${tid} Plan\n\nTask plan stub for testing.\n`);
+  }
 }
 
 function writeContinue(base: string, mid: string, sid: string, content: string): void {

src/resources/extensions/gsd/tests/integration-mixed-milestones.test.ts

@@ -42,6 +42,7 @@ function writeRoadmap(base: string, mid: string, content: string): void {
 function writePlan(base: string, mid: string, sid: string, content: string): void {
   const dir = join(base, '.gsd', 'milestones', mid, 'slices', sid);
   mkdirSync(join(dir, 'tasks'), { recursive: true });
+  writeFileSync(join(dir, "tasks", "T01-PLAN.md"), "# T01 Plan\n");
   writeFileSync(join(dir, `${sid}-PLAN.md`), content);
 }
 

src/resources/extensions/gsd/tests/replan-slice.test.ts

@@ -40,6 +40,7 @@ function writeRoadmap(base: string, mid: string, content: string): void {
 function writePlan(base: string, mid: string, sid: string, content: string): void {
   const dir = join(base, '.gsd', 'milestones', mid, 'slices', sid);
   mkdirSync(join(dir, 'tasks'), { recursive: true });
+  writeFileSync(join(dir, "tasks", "T01-PLAN.md"), "# T01 Plan\n");
   writeFileSync(join(dir, `${sid}-PLAN.md`), content);
 }