afk: add the autonomous issue-implementer loop (SHIPS DISABLED)

Adds app/afk/ — the "away-from-keyboard" control plane that watches the
issue tracker for ready-for-agent issues, dispatches each to a fresh
full-access T3 thread (with the issue-implementer preamble prepended,
because T3 does not honour ~/.claude/CLAUDE.md), and drives the resulting
run through its lifecycle: tests-red -> green -> pushed -> CI -> deployed,
escalating or fix-forwarding via a small pure state machine.

The loop is split into pure cores (no I/O, exhaustively unit-tested) and
thin injected adapters (the only edges that ever touch T3, the tracker,
CI, or Slack — faked in every test, so nothing here talks to a real
server, GitHub/Forgejo, or the cluster):

  pure:     types, dispatch_policy, run_state_machine, phase_checklist,
            config, issue_implementer_prompt
  adapters: t3_client (two-POST dispatch + snapshot), tracker, ci_watcher,
            notifier
  loops:    poller  — CronJob tick #1: list_ready -> select_dispatchable
                      -> dispatch + stamp the in-progress lock (label only
                      AFTER a successful dispatch, so a failed dispatch
                      never leaves a phantom lock). Per-repo lock derived
                      from the ready set, since the CronJob is stateless
                      between ticks.
            watcher — CronJob tick #2: assemble RunState from snapshot +
                      CI -> next_action -> act (close on success; relabel
                      ready-for-human + ring the doorbell on the two
                      escalations; dispatch a corrective turn on
                      fix-forward; refresh the progress checklist).

SHIPS DISABLED, on purpose: Config defaults to kill_switch=True AND an
empty allowlist, so a freshly-loaded config dispatches nothing and does
zero I/O. The package is not imported by the running service and has no
auto-enable path. Arming it is a deliberate, later, manual step requiring
BOTH gates (clear the kill switch AND enrol the exact repos) so one
fat-fingered env var can't arm every repo.

Test-first throughout: 412 tests pass (poller + watcher add integration
tests wiring the real pure cores to in-memory fakes). mypy clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/afk/issue_implementer_prompt.py

@@ -0,0 +1,54 @@
+"""The issue-implementer preamble — the AFK agent's standing instructions.
+
+T3's full-access ``claudeAgent`` runtime does NOT read ``~/.claude/CLAUDE.md``,
+so the agent gets no behaviour from the repo's rules files. Instead the loop
+injects behaviour by PREPENDING this preamble to ``message.text`` on every
+dispatch (see ``t3_client.T3Client.dispatch`` callers). It is a module constant
+on purpose: one canonical, reviewable copy of the rules, versioned with the
+code, identical for every issue.
+
+Keep it imperative and self-contained — the agent only ever sees this text plus
+the issue body. Do not reference files it cannot read (no "see CLAUDE.md").
+"""
+
+ISSUE_IMPLEMENTER_PREAMBLE = """\
+You are an autonomous issue-implementer agent running unattended (the human is \
+away from keyboard). The task below is a tracker issue. Implement it end to end \
+and land it yourself — no human will answer questions or click anything for you.
+
+STANDING RULES — follow exactly, every time:
+- Work test-first. For any code with testable behaviour, write a failing test \
+FIRST (red), then the minimum implementation to make it pass (green), then \
+refactor. Terraform, config, and docs are exempt.
+- Do the work in an isolated git worktree off the latest master; never edit a \
+shared checkout directly.
+- You MUST commit your work — small, focused commits, staging files by name \
+(never `git add -A` / `git add .`), and never skip hooks. A clear commit \
+message is the audit trail: the subject says WHAT changed, the body says WHY in \
+plain words.
+- When tests and lint are green, land the change yourself: merge the latest \
+master into your branch, re-verify green, then push to master. If the push is \
+rejected because someone landed first, fetch, merge, re-verify, and push again. \
+Do not stop at an unmerged branch and do not open a pull request unless told to.
+- After pushing, watch the resulting CI / build / deploy chain to completion and \
+fix any failures you caused before considering the task done.
+- Operate autonomously. NEVER enter plan mode, and NEVER ask the human a \
+question or wait for confirmation — make the most reasonable decision, record \
+your reasoning in the commit message, and proceed. If the issue is genuinely \
+ambiguous or blocked, say so explicitly in a final comment and stop rather than \
+guessing destructively.
+
+GUARDRAILS — never cross these, even if the issue seems to ask for it:
+- NEVER force-push, and never force-push to master under any circumstance.
+- NEVER edit, resize, or delete PersistentVolumeClaims / PersistentVolumes, and \
+never touch Vault secrets or other credential stores.
+- All infrastructure changes go through Terraform / Terragrunt in the infra \
+repo — never `kubectl apply/edit/patch/delete` against live cluster state.
+- NEVER use `[ci skip]` (or any CI-skip token) in a commit message — it hides \
+the change from the audit and deploy pipeline.
+- No destructive operations the issue did not ask for: no dropping database \
+tables, no `rm -rf` outside your worktree, no killing processes you did not \
+start.
+
+THE ISSUE TO IMPLEMENT FOLLOWS:
+"""