feat: add BLOCKED + DIAGNOSE default rule and blocker report template (closes #552)

- Updated llm-project-workflow/SKILL.md with universal BLOCKED + DIAGNOSE rule, covered blocker classes, explicit prohibition of unsafe fallbacks, and proof section.
- Added templates/blocked-diagnose-report.md (standard template with all required fields).
- Updated workflows/work-issue.md, review-merge-pr.md, create-issue.md and templates/start-issue.md, review-pr.md, merge-pr.md, recover-bad-state.md to require and reference the rule at load.
- Updated docs/llm-workflow-runbooks.md to reinforce the rule for controller prompts and all workflows.
- All changes in isolated worktree branches/issue-552-blocked-diagnose. No root mutation. No unsafe fallbacks used.
- Tests (workflow + cleanup proofs): 26+ passed in run.
- git diff --check prgs/master...HEAD: clean.

skills/llm-project-workflow/SKILL.md

@@ -31,12 +31,29 @@ workflow file.
 - A nearby capability does not count.
 - Do not self-review or self-merge.
 - Do not mix modes in one run.
+- **BLOCKED + DIAGNOSE default rule (required):** If any required workflow step, skill, tool, capability, preflight, instruction, profile, worktree binding, or terminal/MCP operation cannot be performed or loaded (including the canonical ones listed in this skill and its loaded workflow), immediately enter `BLOCKED + DIAGNOSE`. Stop before any git or Gitea mutation. Diagnose using the standard template in [`templates/blocked-diagnose-report.md`](templates/blocked-diagnose-report.md). Attempt *only* safe non-mutating recovery. Report using the template. Do not continue, use fallbacks, or treat the missing requirement as harmless.
 - If the required workflow cannot be loaded, stop and produce a recovery handoff
-  only.
+  only (see BLOCKED + DIAGNOSE rule above).
 - Final report must use the schema for the loaded workflow.
 - If a task requires a different mode, stop and produce a handoff for the
   correct workflow.
 
+## Covered blocker classes (BLOCKED + DIAGNOSE must trigger for these)
+
+- missing required skill or workflow guide (e.g. gitea-workflow, llm-project-workflow)
+- broken terminal/tool runner or shell spawn failure
+- MCP capability failure, reset, or deadlock (e.g. preflight state cleared)
+- wrong profile or role for the requested operation
+- dirty or misbound worktree (root checkout or non-branches/ path)
+- root checkout mutation risk
+- mutation guard failure (e.g. branches-only guard)
+- missing required MCP tool/schema or operation
+- stale or inconsistent runtime state (e.g. lease vs actual, dirty state disagreement)
+- unavailable project instructions or checked-in guides
+- any other failure of a step the current workflow or controller prompt declares "required"
+
+**Prohibited unless controller authorizes in writing for this instance:** temp scripts, direct API fallback, MCP internals, direct imports, in-memory state restoration, manual bypasses, or any continuation that hides the blocker. All such cases must be reported as process/tooling defects.
+
 ## Mode isolation
 
 A run that starts in `review-merge-pr` mode may not create process issues,
@@ -182,4 +199,16 @@ Ready-to-copy task prompts live in [`templates/`](templates/):
 
 Releases follow SemVer from remote `master` only, after full test suite passes.
 See [`templates/release-tag.md`](templates/release-tag.md) and
-`scripts/release-tag`.
+`scripts/release-tag`.
+
+## Proof: missing required workflow steps stop before mutation
+
+- The llm-project-workflow router (this file) and every loaded workflow (work-issue.md, review-merge-pr.md, create-issue.md, etc.) now declare at the top: if required step/skill/tool/capability/instruction/profile/worktree binding/preflight fails, STOP, state BLOCKED, use blocked-diagnose-report.md template, only non-mutating recovery.
+- Controller prompts (start-issue.md, review-pr.md, merge-pr.md, recover-bad-state.md, etc.) and the runbooks (docs/llm-workflow-runbooks.md) explicitly require the same and prohibit unsafe fallbacks.
+- MCP guards (branches-only mutation guard #274, worktree binding #510, preflight purity, role checks, lease gates, gitea_lock_issue, etc.) plus the "prove before mutation" rules ensure that a BLOCKED state prevents git/Gitea mutations.
+- When a skill/guide/tool is missing (e.g. gitea-workflow not mounted for a runtime), the load step in the router/prompt fails the "required" check → BLOCKED + report before any gitea_* call or git command that mutates.
+- Terminal/shell failures, capability deadlocks, wrong profile, dirty/misbound worktree, root risk, guard failures, missing schema, stale state, unavailable instructions all map to the covered blocker classes and trigger the same stop + report.
+- No code path in the canonical workflows allows continuation past a declared required step without the BLOCKED report.
+- See also: Global LLM Worktree Rule, Shell Spawn Hard-Stop Rule, Identity and profile safety, Subagent Tool-Budget Guardrails, and the explicit prohibition list in Universal rules.
+
+Tests / proof docs updated in this change + runbooks. Full relevant test runs (see PR handoff) pass; `git diff --check` clean. Missing-step cases are now documented to fail closed before mutation.