fix(ultraplan-local): Bug 3 producers — frontmatter writes + ESM/CJS fix

Step 7 of v3.4.1 plan.

ultraplan-end-session-local Phase 3:
- Replace require()-of-ESM-module shim with node --input-type=module + import.
- Convert Phase 1 project enumeration to ESM as well so the file is uniformly
  ESM (grep -c 'require(' commands/ultraplan-end-session-local.md → 0).
- Combined ESM block writes both .session-state.local.json (atomicWriteJson)
  and sibling NEXT-SESSION-PROMPT.local.md (writeFileSync) so producers
  succeed or fail together.
- Sibling markdown gets frontmatter: produced_by, produced_at, project.

ultraexecute-local Phases 8 / 2.55 / 4:
- Each phase that writes .session-state.local.json now also writes a sibling
  NEXT-SESSION-PROMPT.local.md with frontmatter (produced_by:
  ultraexecute-local, produced_at: ISO-8601, status). Phase 8 includes the
  full ESM block; 2.55 / 4 reference the combined pattern.
- This is the producer side of the Bug 3 contract; consumer-side wire-up
  (Phase 1.5 consistency check in /ultracontinue) lands in Step 8.

Tests: 346 green (no new tests this step — coverage comes via Step 8
integration test).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plugins/ultraplan-local/commands/ultraexecute-local.md

@@ -414,6 +414,11 @@ Verify with `node lib/validators/session-state-validator.mjs --json
 {project_dir}/.session-state.local.json`. On validator failure, emit a warning
 to stderr but do NOT block the stop; `progress.json` is still authoritative.
 
+**Also write sibling `NEXT-SESSION-PROMPT.local.md`** with frontmatter
+(`produced_by: ultraexecute-local`, `produced_at: <ISO-8601>`,
+`status: stopped`) so the next-session producer-mismatch check has both
+candidates available. Use the same combined ESM block pattern as Phase 8.
+
 ### Check 2 — Plan file is tracked by git
 
 Run `git ls-files --error-unmatch {plan-path} 2>/dev/null`. If the plan file is
@@ -898,6 +903,11 @@ the failed entry-condition session was supposed to consume. This lets
 write pattern + validator check as Phase 2.55. On validator failure, warn
 but do not block.
 
+**Also write sibling `NEXT-SESSION-PROMPT.local.md`** with frontmatter
+(`produced_by: ultraexecute-local`, `produced_at: <ISO-8601>`,
+`status: stopped`) — same combined ESM pattern as Phase 8 — so Phase 1.5
+of `/ultracontinue` can compare project-dir and plugin-root candidates.
+
 If the entry condition **passes**:
 ```
 Entry condition: PASS
@@ -1340,6 +1350,27 @@ Use `lib/util/atomic-write.mjs` (`atomicWriteJson`) — same crash-safety as
 --json {project_dir}/.session-state.local.json`. On validator failure, warn
 to stderr but do NOT block — Phase 8 must always reach the final report.
 
+**Also write sibling `NEXT-SESSION-PROMPT.local.md`** (Bug 3 frontmatter
+contract — see `docs/HANDOVER-CONTRACTS.md` § Handover 7 Lifecycle) in the
+project directory. The frontmatter MUST contain `produced_by: ultraexecute-local`
+and `produced_at: <ISO-8601>` so `/ultracontinue` Phase 1.5 can detect
+producer drift between project-dir and plugin-root candidates. Use a single
+ESM inline block so state-file + prompt-file writes succeed or fail together:
+
+```bash
+!`node --input-type=module -e "
+import path from 'node:path';
+import { writeFileSync } from 'node:fs';
+import { atomicWriteJson } from './lib/util/atomic-write.mjs';
+const [, dir, briefPath, label, status] = process.argv;
+const now = new Date().toISOString();
+const stateObj = { schema_version: 1, project: dir, next_session_brief_path: briefPath, next_session_label: label, status, updated_at: now };
+atomicWriteJson(path.join(dir, '.session-state.local.json'), stateObj);
+const promptBody = '---\\nproduced_by: ultraexecute-local\\nproduced_at: ' + now + '\\nproject: ' + dir + '\\nstatus: ' + status + '\\n---\\n\\n# ' + label + '\\n\\nResume via /ultracontinue.\\n';
+writeFileSync(path.join(dir, 'NEXT-SESSION-PROMPT.local.md'), promptBody);
+" '{project_dir}' '{next_session_brief_path}' '{next_session_label}' '{status}'`
+```
+
 This single insertion covers every multi-session execution path that
 converges here (Path A: successful single session, Path B: `--session N`
 explicit, Path C: compaction-survival recovery, Path D: standard plan