Tasks: mark every body the-loop posts (issue-104)

Phase 3 of 3. Derived from the locked design.md. TDD (tdd.mode: standard): the failing test comes first for every behavioural task.

DAG

flowchart LR
    T1[T1 authz helper tests] --> T2[T2 mark_self_authored]
    T2 --> T3[T3 announcement body test]
    T3 --> T4[T4 mark the announcement]
    T4 --> T5[T5 poll regression]
    T4 --> T6[T6 router regression]
    T5 --> T7[T7 lint/typecheck/tests]
    T6 --> T7
    T7 --> T8[T8 docs: reference + capabilities]
    T8 --> T9[T9 PR + reviewer briefing]

Tasks

• [x] T1 — Failing authz unit tests (cli/tests/test_poller.py, beside the existing is_self_authored cases): a marked body carries the visible attribution and the marker and satisfies is_self_authored; marking twice is byte-identical to marking once; the original text survives verbatim. (AC1, AC3)
• [x] T2 — SELF_COMMENT_ATTRIBUTION + mark_self_authored in cli/the_loop/authz.py, immediately after is_self_authored, with the "only ever on text the-loop composed" rule in the docstring. (AC1, AC3, AC4)
• [x] T3 — Failing announcement test (cli/tests/test_announce.py): announcement_body(session) is is_self_authored, and still contains the tmux target, harness name, both attach commands and the retention note. (AC2, AC7)
• [x] T4 — Mark the announcement: announcement_body returns mark_self_authored(...); module docstring records why. (AC1, AC2)
• [x] T5 — Poll-path regression (cli/tests/test_poller_integration.py, Gherkin docstring + Requirement: link): a known work item whose thread gained the-loop's own announcement forwards nothing into the session and resolves the comment. Fails before T4. (AC5, AC7)
• [x] T6 — Webhook-path regression (cli/tests/test_routing.py): an issue_comment event whose body is the announcement is dropped before dispatch. Fails before T4. (AC6, AC7)
• [x] T7 — Full gate from the repo root: ruff check, ruff format --check, markdownlint, pyright, pytest. Record the red→green evidence in the execution log. (AC7)
• [x] T8 — Documentation: skills/the-loop/reference/collaboration.md (the rule covers the CLI daemon's own comments, not only harness replies), docs/capabilities/webhook-triggers.md and docs/capabilities/interactive-sessions.md (current behaviour + history rows). (AC8)
• [x] T9 — PR + reviewer briefing from skills/the-loop/templates/pr-briefing.md; execution log finalised; label → loop:needs-review. (ready-to-ship gate)

Verification

Every task's evidence is its test command's red→green transition, recorded in execution-log.md. The work item is ready to ship when the full gate above is green, the capability docs are updated in this same PR, the security review is recorded, and the briefing is posted.