gate: intuitive wake-rule composition (closes #105)

[antra-tess]

Closes #105. Implements all four pieces, authorized by antra in #operating_room tonight ("Yes, please implement and deploy") after the Mythos stand-back-density incident.

What changed

① passthrough: true observer rules — on the counting behaviors (passive_sample, rate_limit): a matched rule that doesn't fire counts the event and evaluation continues to later policies; when it fires it consumes as usual. evaluate() now runs an inline match/decide loop (first terminal match wins; passthrough non-fires accumulate in decision.observed and the gate:decision trace). Validation rejects the flag on always/defer/skip/debounce.

② Shadow lint — findShadowedPolicies() does conservative per-event-type subsumption over the match language (scope overlap, glob equal-or-absent-or-*, OR-list subset for metadataTrue/tagsAny, constraint subset for tagsAll/tagsNone, identical filter). Every warning is a provably true "rule X makes rule Y unreachable for "; no warning ≠ proven safe. Surfaced in the wake_add_rule result, as a gate:shadow-warnings trace on any config change (startup/reload/mutation, fingerprinted so unchanged sets don't re-trace), and in gate_status.

③ Dry-run probes — EventGate.probe() / probeTable(): side-effect-free evaluation (no counter/bucket mutation, no stats/traces, no debounce batching; sleep and gate.js deliberately ignored). wake_add_rule returns a before/after winners table over canonical shapes (dm open/closed, mention open/closed, reply, ambient human/bot, heartbeat) with changed rows flagged. The incident would have shown dm (open channel): discord-direct-address → stand-back-density, wouldWake false at install time.

④ Anchored positions — addPolicy accepts {before: name} / {after: name} (tool fields insertBefore / insertAfter, mutually exclusive with position); a missing anchor throws naming the available rules. Replacement without placement stays in place (unchanged); replacement WITH placement moves the rule — the repair path for a mis-placed rule. Tool description rewritten: ordering-is-semantics warning, steer to anchors/passthrough, prepend demoted to "only when it must beat everything".

Compat

• addPolicy/addGatePolicy signatures widen (existing 'append'/'prepend' callers unaffected; ChannelModeModule untouched).
• GateStatus gains shadowWarnings: string[]; GateDecision gains optional observed.
• No behavior change for configs without passthrough — the evaluate loop is first-match-wins exactly as before.

Tests

New test/event-gate-passthrough.test.ts (17 tests) covering all four pieces, including the exact incident config shape, the passthrough fix, the probe-table diff that makes it visible, and the anchored-reissue repair. All 7 pre-existing gate suites green individually (100 tests); full suite 558 tests, 0 fail.

🤖 Generated with Claude Code

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