feat(governor): Lane H PR-4 — PressureBroker → governor pure-function bridge

[joelteply]

Summary

Pure-function bridge between PressureBroker's PressureAlert surface (disk/memory pool eviction events) and the governor's typed PressureSignal cascade input. Per GENOME-FOUNDRY-SENTINEL.md Part 11 line 1121: "PressureBroker informs the SubstrateGovernor. Pressure signals from the broker drive the governor's adjustment cascade."

Scope

• alert_to_signal(&PressureAlert) -> Option<PressureSignal> — pure mapping. High/Critical tier → SystemMemHigh{used_pct}; Normal/Warning/unknown → None.
• governor_alert_sink(Arc<dyn SubstrateGovernor>) -> AlertSink — factory that wraps a governor as an AlertSink the broker can register via PressureBroker::add_alert_sink. Sink derives the signal and forwards via governor.on_pressure_signal when Some; drops when None.

NOT in this PR (deferred)

• Wiring the sink into PressureBrokerModule's boot path — separate concern. The bridge is the data-side primitive; wiring is PR-5.
• Pool-name-aware mapping (vram → VRAMHigh, docker → potential DiskHigh variant). Today's broker pools are all memory-adjacent (Docker disk, HF cache, future VRAM via GpuMemoryManager); SystemMemHigh is the conservative single-mapping the cascade reacts to identically. Refinement when pool tier_name conventions stabilize.

Discipline

• No silent default-on-error. Mapping is total — every alert maps to either Some(signal) or None explicitly.
• Pressure clamped to [0.0, 1.0] before percent conversion so transient over-budget snapshots map to 100% and negative artifacts map to 0% rather than wrapping via as u8.
• Sink forwards via Arc<dyn SubstrateGovernor> (object-safe trait) so the bridge does not depend on LocalSubstrateGovernor concretely.

Tests (14, all passing)

• normal/warning/unknown tiers → None (4 tests)
• high/critical tiers → SystemMemHigh with rounded used_pct (3 tests)
• pressure clamping above 1.0 + below 0.0 + rounding (3 tests)
• sink forwarding high/critical + non-forwarding normal/warning (4 tests)
• sink survives construction-scope drop + multi-call ordering (2 tests)

Full governor suite: 152 passing (138 prior + 14 new).

Lane H 8-PR stack progress

PR-1 (#1330/1331) → PR-2 (#1345) → PR-3a (#1352) → PR-3b (#1354) → PR-3c1 (#1356) → PR-3c2 (#1360) → PR-3c3 (#1364) → PR-3c4 (#1365) → PR-4 (this PR). PR-3d governor file watcher in flight from codex (#1368, parallel branch, no overlap).

Test plan

• cargo test --package continuum-core --lib --features metal,accelerate governor::pressure_bridge:: — 14/14 pass
• cargo test --package continuum-core --lib --features metal,accelerate governor:: — 152/152 pass (no regressions)
• Pre-push TS clean, ESLint baseline held, Rust compile clean
• CI green (will re-run once canary TS hotfix from codex lands)

🤖 Generated with Claude Code