docs: capture AFK implementation pipeline design + ADRs 0002-0004

Record the architecture for moving code implementation AFK, decided in a
design/grilling session. The owner wants the human-in-the-loop boundary to
stop at design + spec: once an issue is triaged ready-for-agent, an agent
should implement it test-first, push it, and see it to a healthy deploy on
its own, escalating only when it can't proceed.

Decisions captured:
- claude-agent-service is the control plane (poller + watcher + safety);
  a dedicated in-cluster T3 Code instance is the executor + cockpit, because
  T3 can only show sessions it launched itself -> we dispatch into it
  (ADR 0003).
- AFK code pushes straight to master; on a broken deploy it fix-forwards
  then freezes the broken state for forensics rather than reverting
  (ADR 0002).
- Implementation agents use persistent per-repo checkouts + git worktrees on
  SSD-NFS for warm caches, reversing the throwaway-clone rule for this path
  because concurrency is serial-within-repo (ADR 0004).

Pilot-gated: five integration unknowns must be validated against a dedicated
T3 instance before the poller is wired. No code yet.

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

docs/adr/0003-t3-thin-executor-and-cockpit.md

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+# AFK workers run inside a dedicated T3 Code instance; claude-agent-service dispatches into it
+
+The owner wants one UI to see and converse with every in-flight AFK worker, and
+named **T3 Code** (the self-hosted multi-agent cockpit already running at
+`t3.viktorbarzin.me`) as that UI. Research into T3's source
+(`pingdotgg/t3code`, ~v0.0.27) found it is genuinely built for this — a fleet of
+worker "threads" with a live read-model and a scoped HTTP dispatch API — **but**
+it can only display sessions **it launched itself**; there is no command to adopt
+a session another process started. So "viewable in T3" ⟺ "launched by T3". This
+ADR records the resulting architecture: `claude-agent-service` stays the
+**control plane** and **dispatches into a dedicated, in-cluster T3 instance**
+which is the **executor + cockpit**. The agent runs inside T3; we keep the brain.
+
+## Status
+
+accepted (2026-06-14) — direction decided; **gated on a pilot** (the five
+unknowns in the design doc) before the poller is wired and the architecture is
+committed.
+
+## Why T3, and why "thin"
+
+T3 provides, out of the box, what we would otherwise hand-build: a three-panel
+fleet cockpit (`projects → threads → conversation`), an
+`OrchestrationReadModel` with per-thread live status, and
+`POST /api/orchestration/dispatch` whose `thread.turn.start` + `bootstrap` can
+**create a thread, prepare a git worktree, run a setup script, and deliver a
+prompt in one call** — exactly the worker-spawn primitive. Converse / approve /
+resume are native (`thread.user-input.respond`, `thread.approval.respond`). For
+Claude it embeds `@anthropic-ai/claude-agent-sdk`.
+
+"Thin" = the AFK *behavior and safety* (the `issue-implementer` prompt,
+guardrails, always-push, fix-forward/freeze, CI-watch, issue integration) live
+in **our** layer (the poller + watcher), not in T3. T3 is a **swappable backend**
+we drive over its API.
+
+## Considered options
+
+- **Thin: claude-agent-service dispatches into T3 (chosen).** Control plane calls
+  T3's dispatch API; T3 runs the agent in a worktree and shows it. Get the fleet
+  view, keep the brain, least to build. Cost: execution moves into the T3 pod, so
+  T3's runtime is in the *hot path* (not just the window).
+- **claude-agent-service runs the agent, T3 only displays it** — rejected because
+  it is impossible: T3 cannot adopt an externally-started session
+  (`thread.session.set` is server-internal; no external-session-id field). This
+  is the constraint that shaped the whole decision.
+- **Deep: claude-agent-service as a custom T3 provider (ACP-style)** — rejected
+  for now: keeps the runtime ours with a T3 UI, but means building and
+  maintaining a provider against a pre-1.0, internal, no-contributions interface
+  — effectively a fork. Revisit only if "thin" proves too limiting.
+- **Skip T3; build our own console** (generalized breakglass + tmux) — rejected:
+  most stable and fully in-house, but abandons the owner's explicit "see workers
+  in T3" goal and means owning a session console forever.
+
+## Consequences
+
+- A **dedicated in-cluster T3 instance** (a pod, consistent with the earlier
+  in-cluster-over-devvm substrate choice) is the worker host, separate from the
+  per-user devvm T3 instances. It needs the SSD worktree volume, git/Anthropic
+  tokens, toolchains, `claude auth`, and an internal Authentik-gated ingress.
+- T3's runtime is now in the **execution hot path** — its maturity affects
+  whether work *runs*, not only whether it can be *seen*. Mitigations: **pin the
+  version and exclude it from Keel** (its churn + hard-cutover auth migrations
+  make auto-upgrade a Keel-class hazard), keep the integration thin and the
+  backend swappable, and **pilot** the five unknowns first.
+- T3 is **single-operator** — fine here: it matches the already-accepted shared
+  service identity for AFK work.
+- No outbound webhooks from T3 → the watcher **polls**
+  `GET /api/orchestration/snapshot`.
+- This supersedes the intermediate ideas of evolving `claude-agent-service` into
+  its own session/tmux/worktree runtime and building a bespoke attach console.