feat(boss): bolder autonomous /boss — grounding-PASS auto-sign, rollback sandbox, reference issue

Retire the obligatory five-lens spec-skeptic auto-sign panel (worst case
18 agent runs per spec under /boss). The autonomous signature is now the
Step-5 grounding-check PASS alone — an independent fresh-context agent's
verdict against currently-green tests; a no-override BLOCK/INFRA_ERROR
routes to the human sign-off pause.

The judgement the panel applied moves upstream into specify Step 1.5,
whose stance inverts: a load-bearing fork the orchestrator can DERIVE an
answer for (sources, code, consistency, risk) is decided boldly and
recorded on the run's reference issue; only a pure-preference fork
bounces. spec-skeptic survives as an optional ad-hoc bias-breaker the
orchestrator pulls when unsure whether its leaning is judgement or bias —
not a gate, not a veto.

Every /boss run carries a mandatory reference issue (created if the cycle
had none): the fork-decision log, the orchestrator's cross-run memory,
and the only surviving trace of a hard-dropped attempt.

Relax main-sacrosanct below the session anchor: within an autonomous run
the orchestrator may git reset --hard its OWN UNPUSHED commits above the
anchor on a dead end — never below the anchor, never a pushed commit
(forward-only/revert). Discarded attempts are hard-dropped, no parking.

Verified across the 9 edited files by a 4-lens adversarial review
(retired-panel residue, cross-file contracts, rollback-boundary safety,
stance coherence): unanimous SOUND. Baseline tagged pre-autosign-rework.

closes #8

docs/design.md

@@ -53,8 +53,12 @@ The plugin owns:
   states.
 - **Working-tree-as-quarantine** — agents write artefacts to
   the working tree, never commit. Only the orchestrator commits.
-- **main HEAD sacrosanct** — no reset, no revert, by any actor.
-  main moves forward only via orchestrator commits.
+- **main HEAD sacrosanct below the session anchor** — no reset, no
+  revert of user-ratified history, by any actor; main moves forward only
+  via orchestrator commits. The one narrow exception is the `/boss`
+  rollback sandbox: the orchestrator may wind back its *own* unpushed
+  autonomous commits above the run's start anchor (`boss/SKILL.md`
+  § Direction freedom).
 - **No nested subagent dispatch** — a hard Claude Code platform
   constraint: an agent cannot spawn further agents. Workflows do not
   lift it; a workflow script orchestrates from the **top level**, and