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

plugins/ultraplan-local/commands/ultraplan-end-session-local.md

@@ -63,7 +63,7 @@ Resolve the nearest `.claude/projects/*/brief.md` from cwd (the current working
 directory). Use `node -e` enumeration (NOT shell glob — harness-mode safety):
 
 ```bash
-!`node -e "const fs=require('fs'),path=require('path');const root='.claude/projects';if(!fs.existsSync(root)){process.exit(0)}const dirs=fs.readdirSync(root).filter(d=>fs.existsSync(path.join(root,d,'brief.md'))).map(d=>path.join(root,d));dirs.forEach(p=>process.stdout.write(p+'\\n'));"`
+!`node --input-type=module -e "import {existsSync, readdirSync} from 'node:fs'; import {join} from 'node:path'; const root='.claude/projects'; if(!existsSync(root)) process.exit(0); readdirSync(root).filter(d=>existsSync(join(root,d,'brief.md'))).forEach(d=>process.stdout.write(join(root,d)+'\\n'));"`
 ```
 
 Decision tree:
@@ -89,7 +89,7 @@ Print to stderr and exit 1. **No interactive prompt** — this keeps the helper
 headless-safe (per brief NFR; addresses adversarial-review major #11). If you
 want an interactive flow, use `/ultracontinue --help` to see the full pipeline.
 
-## Phase 3 — Atomically write `.session-state.local.json`
+## Phase 3 — Atomically write `.session-state.local.json` + sibling NEXT-SESSION-PROMPT.local.md
 
 Write `<project-dir>/.session-state.local.json` with the schema-v1 object:
 
@@ -105,21 +105,37 @@ Write `<project-dir>/.session-state.local.json` with the schema-v1 object:
 ```
 
 Use the atomic-write util — write to `<path>.tmp`, then `rename` into place —
-to avoid partial-state on crash. Inline-call pattern:
+to avoid partial-state on crash. The util is ESM, so invoke via
+`node --input-type=module -e` with an `import` statement (a CommonJS shim
+would throw `ERR_REQUIRE_ESM` on Node 18+ since `atomic-write.mjs` is ESM).
+
+Under `node --input-type=module -e "<script>" arg1 arg2 arg3`, Node sets
+`process.argv[0]` to the node binary path and user args start at
+`process.argv[1]`. Adjust the destructure if your Node version differs.
+
+This phase ALSO writes a sibling `NEXT-SESSION-PROMPT.local.md` in the
+project directory with YAML frontmatter (`produced_by: ultraplan-end-session-local`,
+`produced_at: <ISO-8601>`, `project: <project-dir>`). Both files are written
+in a single ESM block so the writes succeed or fail together:
 
 ```bash
-!`node -e "
-const path=require('path');
-const {atomicWriteJson}=require('./lib/util/atomic-write.mjs');
-const obj={schema_version:1,project:process.argv[1],next_session_brief_path:process.argv[2],next_session_label:process.argv[3],status:'in_progress',updated_at:new Date().toISOString()};
-atomicWriteJson(path.join(process.argv[1],'.session-state.local.json'),obj);
-console.log(path.join(process.argv[1],'.session-state.local.json'));
+!`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, brief, label] = process.argv;
+const now = new Date().toISOString();
+const stateObj = { schema_version: 1, project: dir, next_session_brief_path: brief, next_session_label: label, status: 'in_progress', updated_at: now };
+const stateFile = path.join(dir, '.session-state.local.json');
+atomicWriteJson(stateFile, stateObj);
+const promptFile = path.join(dir, 'NEXT-SESSION-PROMPT.local.md');
+const promptBody = '---\\nproduced_by: ultraplan-end-session-local\\nproduced_at: ' + now + '\\nproject: ' + dir + '\\n---\\n\\n# ' + label + '\\n\\nResume via /ultracontinue.\\n';
+writeFileSync(promptFile, promptBody);
+console.log(stateFile);
+console.log(promptFile);
 " '<project-dir>' '<next-brief-path>' '<next-label>'`
 ```
 
-(Note: `atomic-write.mjs` is ESM; if the inline `require()` form fails in your
-Node version, fall back to `node --input-type=module -e "..."` with `import`.)
-
 ## Phase 4 — Validate + narrate
 
 Validate the freshly-written state file: