feat(graceful-handoff): 2.0 — migrate to skills/ with disable-model-invocation [skip-docs]

Step 1 of v2.0 plan. Hard cut from commands/ to skills/ per Anthropic
recommendation for new plugins. Frontmatter sets disable-model-invocation:
true and pins model: claude-sonnet-4-6. Docs (README, CLAUDE.md, root
README) deferred to Step 9 per plan.

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

@@ -460,11 +460,25 @@ After the loop exits (pass, cap, or force-stop), ensure:
 Populate the "How to continue" footer with the actual project path and
 topic questions.
 
+**Schema sanity check (since v3.1.0):** before reporting, run the brief
+validator. This catches frontmatter typos and state-machine inconsistencies
+the brief-reviewer rubric does not check (e.g. `research_status: skipped`
+with `research_topics: 3` and no `brief_quality: partial`).
+
+```bash
+node ${CLAUDE_PLUGIN_ROOT}/lib/validators/brief-validator.mjs --json "{PROJECT_DIR}/brief.md"
+```
+
+If the validator returns errors, report them to the user and offer to
+re-enter Phase 4 with the validator's hints in scope. If only warnings,
+note them in the final report.
+
 Report:
 ```
 Brief written: {PROJECT_DIR}/brief.md
 Review iterations: {1..3}
 Final quality: {complete | partial}
+Validator: {PASS | warnings(N)}
 Research topics identified: {N}
 ```
 

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

@@ -187,6 +187,23 @@ report. Do NOT run security scan, do NOT touch progress files, do NOT
 execute any steps. This gives the user a fast sanity-check of plan
 schema compliance without side effects.
 
+**Preferred path (since v3.1.0):** invoke the plan validator directly. It
+returns the same diagnostic info Phase 2 derives in prose, with stable
+error codes for downstream tooling:
+
+```bash
+node ${CLAUDE_PLUGIN_ROOT}/lib/validators/plan-validator.mjs --strict --json "{path}"
+
+# When --project is in scope and progress.json exists, also validate it:
+[ -f "{project_dir}/progress.json" ] && \
+  node ${CLAUDE_PLUGIN_ROOT}/lib/validators/progress-validator.mjs --json "{project_dir}/progress.json"
+```
+
+Map the validator's `code` field to the error templates below (e.g.
+`PLAN_FORBIDDEN_HEADING` → "Detected heading format" branch). When both
+calls exit 0, render the READY report. Otherwise render FAIL with the
+validator's first error code + message.
+
 If Phase 2 parsing succeeded (no fatal errors, every step has a valid
 Manifest block in strict mode, or synthesized manifests in legacy mode):
 

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

@@ -61,11 +61,27 @@ Parse `$ARGUMENTS` for mode flags. Order of precedence:
      Missing: {dir}/brief.md
      ```
    - Set **project_dir = {dir}**, **brief_path = {dir}/brief.md**.
+   - **Validate inputs** (soft mode — warnings do not block, errors do):
+     ```bash
+     # Brief schema sanity check (frontmatter + state machine, soft on body sections)
+     node ${CLAUDE_PLUGIN_ROOT}/lib/validators/brief-validator.mjs --soft --json "{dir}/brief.md"
+
+     # Research briefs (if any) — drift-warn only, none of these block the run
+     [ -d "{dir}/research" ] && \
+       node ${CLAUDE_PLUGIN_ROOT}/lib/validators/research-validator.mjs --soft --dir "{dir}/research" --json
+
+     # Architecture note discovery (EXTERNAL CONTRACT — drift-WARN, never drift-FAIL)
+     node ${CLAUDE_PLUGIN_ROOT}/lib/validators/architecture-discovery.mjs --json "{dir}"
+     ```
+     Each call exits 0 on success or with a structured JSON error report on stderr.
+     Surface any warnings in the user-facing summary at Phase 3, but do not abort.
    - Set **has_research_brief = true** if `{dir}/research/*.md` matches ≥ 1 file.
-   - Set **has_architecture_note = true** if `{dir}/architecture/overview.md` exists.
-     If set, **architecture_note_path = {dir}/architecture/overview.md**. Produced by
-     the optional `/ultra-cc-architect-local` command from the separate `ultra-cc-architect`
-     plugin. Missing file is fine — this is additive discovery, not a requirement.
+   - Read the architecture-discovery JSON output: set **has_architecture_note = true**
+     if `found == true`. The discovery module emits warnings if the file lives at a
+     non-canonical path (e.g. `architecture-overview.md`); preserve them for the
+     user-facing summary. If set, **architecture_note_path = {result.overview}**.
+     Produced by the optional `/ultra-cc-architect-local` command from the separate
+     `ultra-cc-architect` plugin. Missing file is fine — additive discovery, not required.
 
 4. **`--brief <path>`** — extract the brief path. If the file does not exist:
    ```