fix(mcp): add sanctioned gitea_edit_issue and a doc/registry drift guard (Closes #781)

The gitea-workflow documentation named a gitea_edit_issue tool that no
namespace had ever registered. There was no sanctioned MCP path to change an
issue title or body at all: the only edit tool, gitea_edit_pr, PATCHes the
pull-request endpoint. An authorized body correction on issue #780 therefore
had to be recorded as a discussion comment instead.

Add edit_issue.py as the authoritative rule and gitea_edit_issue as the tool
built on it:

- Only the fields the caller names are sent, so labels, state, assignee, and
  milestone cannot be overwritten from a stale read.
- A pull-request number is refused. Gitea serves pull requests from the same
  /issues/{n} collection, so without that check the issue path would quietly
  become a second, ungated PR edit path. gitea_edit_pr stays PR-only.
- Structurally invalid requests raise before any credential or network work;
  a request that would change nothing is reported as an explicit no-op with a
  next action rather than a silent success.
- Read-after-write proves the applied title/body and proves that state,
  labels, assignees, and milestone did not move. Transport failures on the
  pre-read, the PATCH, and the read-back are each reported, redacted, with
  the correct performed/verified state.

Gates match every other issue mutation: profile permission via the shared
capability map (resolver task edit_issue, gitea.issue.comment), preflight
purity, branches worktree validation, anti-stomp inventory membership, and
audited mutation.

Fix the drift that hid this. docs/mcp-tool-inventory.md is now the canonical
registered-tool list, and mcp_tool_inventory.py compares it to the live
registry in both directions, plus checks that every tool named under skills/
is registered. The new guard immediately found a second instance of the same
defect: gitea_record_pre_review_command had lost its @mcp.tool() decorator
while the canonical review workflow still instructed reviewers to call it, so
that registration is restored.

Validation:
PASSED: venv/bin/python -m pytest tests/test_issue_781_edit_issue_tool.py -s -q
  — 50 passed
FAILED: venv/bin/python -m pytest -s -q — 4095 passed, 11 failed, 6 skipped.
  The identical 11 tests fail on clean master 8e149e6 with no changes applied
  (254 passed, 11 failed across those five files), so they are pre-existing
  and proven by a baseline run rather than asserted.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

skills/gitea-workflow/SKILL.md

@@ -35,3 +35,11 @@ Install for Codex:
 ```
 
 Preflight via MCP: `mcp_check_workflow_skill_preflight`.
+
+## Tool inventory
+
+Which tools actually exist is documented in
+[`docs/mcp-tool-inventory.md`](../../docs/mcp-tool-inventory.md), which a test
+holds equal to the registered set. Never plan a mutation against a tool that is
+not listed there — that is the #781 failure mode, where a documented
+`gitea_edit_issue` did not exist until execution time.

skills/llm-project-workflow/SKILL.md

@@ -216,6 +216,15 @@ Helpers: `scripts/worktree-start`, `scripts/worktree-review`,
 - Never place raw tokens in LLM/MCP config.
 - Use `gitea_whoami` and `gitea_resolve_task_capability` before mutating.
 
+## Tool inventory
+
+[`docs/mcp-tool-inventory.md`](../../docs/mcp-tool-inventory.md) is the canonical
+list of registered tools, held equal to the live registry by a test. A tool that
+is not listed there does not exist — do not scope work around it (#781).
+
+Issue content is edited with `gitea_edit_issue` (title/body only, read-after-write
+verified). `gitea_edit_pr` is pull-request-only and never accepts an issue number.
+
 ## Controller Handoff
 
 Every task must end with a section titled exactly `Controller Handoff`. Compact