Tasks: remove the process runner — tmux-only dispatch (issue-156)

Phase 3 of 3. Derived from bugfix.md + design.md (both locked). TDD per task; each task names the ACs it delivers.

Task list

• [x] T1 — registry: drop Session.runner (AC2.2). Remove the field from the dataclass, to_dict, from_dict (legacy key ignored on read) and the session.registered event. Update test_tmux_runner.py::TestSessionRunnerFields (round-trip without the field; a legacy record carrying "runner": "process" still parses and is not branched on).
• [x] T2 — runner module: tmux always required, empty target is missing (AC1.3, AC2.4). check_dependencies(web_enabled) — tmux unconditional, ttyd when the web terminal is on; TmuxRunner.deliver reports session_missing for an empty target. Update TestCheckDependencies.
• [x] T3 — harness adapters: remove the headless dispatch surface (AC2.1). Delete HarnessAdapter.resume/spawn/_run/_resume_argv, DispatchResult, _session_id_from_output; rename _spawn_argv → _oneshot_argv (base + claude + cursor); trim harness/__init__ exports. Keep Usage/usage_from_output/parse_json_object/oneshot_argv (critics) and the interactive_* surface. Update test_routing.py adapter tests; keep test_critics.py green.
• [x] T4 — interaction config: drop the runner coupling. Remove the runner parameter and the cli-under-process warning from InteractionConfig.from_mapping; update test_interaction.py.
• [x] T5 — dispatcher: one dispatch plane (AC1.1, AC1.2, AC2.3). RoutingConfig loses runner (leftover key ⇒ warning); _dispatch_one is tmux-only (headless else-branch, no-adapter drop and _log_usage removed); _spawn_for always _spawn_tmux; constructor/reload comments updated.
• [x] T6 — commands + announcer sweep. gh_webhook/poll startup and reload log lines; sessions attach empty-target message; sessions list drops the Runner column; sessions start prints the tmux target; SessionAnnouncer.announce guard becomes not session.tmux_target; poller comment updated.
• [x] T7 — re-host the dispatcher test fleet on the tmux contract. The FakeAdapter dispatch block in test_routing.py and the end-to-end suites (test_webhook_routing_integration.py, test_poller_integration.py, test_control_cli.py, test_announce.py, test_graph_drive*.py) run on the tmux path with the stateful stub tmux; delete tests that pinned the removed behaviour (process defaults, attach-refusal, cli-under-process warning, check_dependencies("process")).
• [x] T8 — new pins (AC2.3, AC2.4, AC4.1). Integration test (Gherkin, linked to AC2.4): an event for a legacy record without tmuxTarget respawns a tmux session resuming the recorded conversation. Unit tests: routing.runner leftover warns and is ignored; spawn needs no runner config to be tmux.
• [x] T9 — config schema + shipped configs (AC2.3, AC3.1). Delete routing.runner from cli-config.schema.json; scrub process-runner prose from neighbouring descriptions (interaction, tmux, webTerminal, announce, defaultHarness); update .the-loop/cli-config.yaml and skills/the-loop/templates/cli-config.yaml.
• [x] T10 — CLI docs (AC3.1). docs/config/cli/routing-options.md (delete ### runner, fix interaction/webTerminal/announce prose — in the same commit as T9: test_docs_parity P3/P4 pin schema↔docs), docs/cli/concepts.md, getting-started.md, installation.md (tmux is now required), index.md, commands/{poll,gh-webhook,sessions}.md, docs/config/cli/{index,polling-options}.md, docs/config/index.md, docs/cli/state.md (registry schema drops runner).
• [x] T11 — capability docs (AC3.2). interactive-sessions.md (tmux is the capability, not an option; mixed-fleet requirement removed), webhook-triggers.md (cli-under-process requirement removed), token-economy.md (cost model no longer a runner tradeoff), process-graph.md, cli.md; history rows added, existing rows untouched.
• [x] T12 — skill references (AC3.1). skills/the-loop/reference/token-economy.md (rewrite the runner-tradeoff framing), automation.md, context.md.
• [x] T13 — decision record. decision-056 (tmux is the only runner; supersedes the runner choice of 021 and the headless dispatch of 016); index row added; 021's index status flipped to superseded (by 056).
• [x] T14 — full gate + evidence (AC4.2). pytest, ruff check+format, pyright, markdownlint, validate_config.py; evidence in the execution log.
• [x] T15 — ship. Self-reviews, push claude/github-issue-156-w0x1bz, PR with reviewer briefing, phase label → loop:needs-review, paper-trail comment on the ticket (with the agent marker).

Dependency graph (DAG)

flowchart TD
    T1[T1 registry] --> T5[T5 dispatcher]
    T2[T2 runner module] --> T5
    T3[T3 adapters] --> T5
    T4[T4 interaction] --> T5
    T5 --> T6[T6 commands sweep]
    T5 --> T7[T7 re-host test fleet]
    T6 --> T7
    T7 --> T8[T8 new pins]
    T9[T9 schema+configs] --> T10[T10 CLI docs]
    T10 --> T11[T11 capability docs]
    T11 --> T12[T12 skill references]
    T12 --> T13[T13 decision record]
    T8 --> T14[T14 full gate]
    T13 --> T14
    T14 --> T15[T15 ship]

Checkpoints

• After T6: package imports clean; unit suites for the touched modules green.
• After T8: full pytest green.
• After T13: markdownlint + validate_config.py + docs-parity tests green.
• After T14: evidence recorded in execution-log.md.

Review comments

• (populated via PR review)