feat(audit): add reaction-rate drift gate thresholds

Add optional reaction match-drop and skip-increase drift thresholds, expose CLI flags, and enable conservative defaults in cadence package scripts. Includes tests and docs/state sync.

README.md

@@ -1644,6 +1644,7 @@ Backend drift/freshness gate for backend-scoped artifacts (`pi_embedded` vs `nat
 ```bash
 pnpm audit:phase0-baseline:live:drift
 ```
+Optional drift thresholds now include reaction decision deltas (`--max-reaction-match-rate-drop-pp`, `--max-reaction-skip-rate-increase-pp`) in addition to run/cancel/error/cancel-latency thresholds.
 This command writes drift reports to:
 - `docs/plans/artifacts/phase0_baseline_live_backend_drift_<UTC-date>.md`
 - `docs/plans/artifacts/phase0_baseline_live_backend_drift_<UTC-date>.json`

docs/api/PROTOCOL.md

@@ -23,7 +23,7 @@ The gateway provides:
 - **HTTP Server**: Serves static dashboard and handles webhook endpoints
 - **Node Capability Negotiation**: Optional companion-node role/capability registration
 
-Operational note: onboarding (`flynn setup` / `flynn onboard`) now runs post-save live readiness checks (model/channel/memory/automation) and prints a guided first-success task flow. Companion CLI now also supports bootstrap-manifest export (`flynn companion --export-bootstrap <path|->`), release-bundle export (`--export-release-bundle <dir>` with optional `--signing-key`/`--signing-key-id` signature output), release-bundle verification (`--verify-release-bundle <dir>` with optional `--verify-signing-key`/`--verify-signing-key-id`/`--require-signature`), platform shell-template export (`--export-shell-template <dir>`), plus richer shell bootstrap flags for status/location/push (`--app-version`, `--latitude/--longitude`, `--push-token`, etc.) for desktop/mobile app packaging without changing JSON-RPC method/event shapes. Audit observability now includes live phase-0 baseline capture flows: `pnpm audit:phase0-baseline:live` for channel-origin windows, backend-scoped variants (`pnpm audit:phase0-baseline:live:pi` / `pnpm audit:phase0-baseline:live:native`) via `--backend`, `pnpm audit:phase0-baseline:live:gateway` (auto-detected cancel window) for gateway-origin windows, `pnpm audit:phase0-baseline:live:refresh` for one-shot refresh of all live windows (channel + gateway + backend-scoped), `pnpm audit:phase0-baseline:live:drift` for backend artifact freshness/drift gates (writing `phase0_baseline_live_backend_drift_<tag>.md/.json` reports), `pnpm audit:phase0-baseline:live:refresh:drift:rolling` for cadence runs that stamp each capture with a unique UTC timestamp tag (`YYYY-MM-DD-HHMMSS`) so drift comparisons can immediately use a prior snapshot (or externally supplied `TAG`), `pnpm audit:phase0-baseline:live:prune` / `pnpm audit:phase0-baseline:live:prune:apply` for rolling-tag artifact retention management (writing `phase0_baseline_live_prune_<tag>.md/.json` reports and retaining those prune reports as part of managed rolling families), and `pnpm audit:phase0-baseline:live:refresh:drift:rolling:prune` for one-command cadence refresh+drift+retention apply reusing the same rolling tag (non-negative integer `KEEP_PER_FAMILY` override supported for retention depth). These scripts default to current UTC-date tags unless `--tag` is explicitly provided.
+Operational note: onboarding (`flynn setup` / `flynn onboard`) now runs post-save live readiness checks (model/channel/memory/automation) and prints a guided first-success task flow. Companion CLI now also supports bootstrap-manifest export (`flynn companion --export-bootstrap <path|->`), release-bundle export (`--export-release-bundle <dir>` with optional `--signing-key`/`--signing-key-id` signature output), release-bundle verification (`--verify-release-bundle <dir>` with optional `--verify-signing-key`/`--verify-signing-key-id`/`--require-signature`), platform shell-template export (`--export-shell-template <dir>`), plus richer shell bootstrap flags for status/location/push (`--app-version`, `--latitude/--longitude`, `--push-token`, etc.) for desktop/mobile app packaging without changing JSON-RPC method/event shapes. Audit observability now includes live phase-0 baseline capture flows: `pnpm audit:phase0-baseline:live` for channel-origin windows, backend-scoped variants (`pnpm audit:phase0-baseline:live:pi` / `pnpm audit:phase0-baseline:live:native`) via `--backend`, `pnpm audit:phase0-baseline:live:gateway` (auto-detected cancel window) for gateway-origin windows, `pnpm audit:phase0-baseline:live:refresh` for one-shot refresh of all live windows (channel + gateway + backend-scoped), `pnpm audit:phase0-baseline:live:drift` for backend artifact freshness/drift gates (including optional reaction-rate thresholds, writing `phase0_baseline_live_backend_drift_<tag>.md/.json` reports), `pnpm audit:phase0-baseline:live:refresh:drift:rolling` for cadence runs that stamp each capture with a unique UTC timestamp tag (`YYYY-MM-DD-HHMMSS`) so drift comparisons can immediately use a prior snapshot (or externally supplied `TAG`), `pnpm audit:phase0-baseline:live:prune` / `pnpm audit:phase0-baseline:live:prune:apply` for rolling-tag artifact retention management (writing `phase0_baseline_live_prune_<tag>.md/.json` reports and retaining those prune reports as part of managed rolling families), and `pnpm audit:phase0-baseline:live:refresh:drift:rolling:prune` for one-command cadence refresh+drift+retention apply reusing the same rolling tag (non-negative integer `KEEP_PER_FAMILY` override supported for retention depth). These scripts default to current UTC-date tags unless `--tag` is explicitly provided.
 
 ### Execution Model (Sessions + Per-Session Queue)
 

docs/architecture/AGENT_DIAGRAM.md

@@ -170,7 +170,7 @@ Gateway streaming UX signals:
 - `pnpm audit:phase0-baseline:live:pi` and `pnpm audit:phase0-baseline:live:native` capture backend-scoped channel windows using `backend.route` timelines.
 - `pnpm audit:phase0-baseline:live:gateway` captures gateway-origin baseline windows by auto-selecting the latest cancel/cancelled session window (or use `scripts/capture-phase0-live-baseline.ts --source gateway --since ... --until ...` for explicit windows).
 - `pnpm audit:phase0-baseline:live:refresh` runs channel + gateway + backend-scoped (`pi_embedded` and `native`) capture commands in one cadence step.
-- `pnpm audit:phase0-baseline:live:drift` evaluates backend-scoped artifact freshness/drift gates and writes `docs/plans/artifacts/phase0_baseline_live_backend_drift_<UTC-date>.md/.json`; `pnpm audit:phase0-baseline:live:refresh:drift` runs capture + drift checks in one cadence step.
+- `pnpm audit:phase0-baseline:live:drift` evaluates backend-scoped artifact freshness/drift gates (including optional reaction match/skip rate thresholds) and writes `docs/plans/artifacts/phase0_baseline_live_backend_drift_<UTC-date>.md/.json`; `pnpm audit:phase0-baseline:live:refresh:drift` runs capture + drift checks in one cadence step.
 - `pnpm audit:phase0-baseline:live:refresh:drift:rolling` runs the same full refresh+drift flow with a shared UTC timestamp tag (`YYYY-MM-DD-HHMMSS`) so each cadence run keeps distinct backend/drift artifacts for immediate baseline-vs-prior comparisons.
 - `pnpm audit:phase0-baseline:live:prune` provides dry-run retention planning for rolling-tag artifacts; `pnpm audit:phase0-baseline:live:prune:apply` deletes older rolling snapshots while keeping the newest tags per artifact family.
 - `pnpm audit:phase0-baseline:live:refresh:drift:rolling:prune` now reuses the rolling refresh+drift pipeline via shared `TAG` env wiring, then applies retention (non-negative integer `KEEP_PER_FAMILY`) and writes prune reports tagged to that same rolling run (`phase0_baseline_live_prune_<tag>.md/.json`).

docs/architecture/GATEWAY_SESSIONS_AND_QUEUE.md

@@ -35,7 +35,7 @@ If you only want the protocol surface, see `docs/api/PROTOCOL.md`.
 - Backend-scoped channel snapshots can be regenerated with `pnpm audit:phase0-baseline:live:pi` / `pnpm audit:phase0-baseline:live:native` (`--backend` filtering via `backend.route` timelines).
 - Gateway-origin phase-0 windows (including cancel-path samples) can be captured with `pnpm audit:phase0-baseline:live:gateway` (auto-detect latest cancel window) or `scripts/capture-phase0-live-baseline.ts --source gateway --since ... --until ...` for explicit bounds.
 - `pnpm audit:phase0-baseline:live:refresh` runs channel + gateway + backend-scoped (`pi_embedded` and `native`) capture paths in one command.
-- `pnpm audit:phase0-baseline:live:drift` checks backend-scoped artifact freshness/drift gates and writes `phase0_baseline_live_backend_drift_<UTC-date>.md/.json`; `pnpm audit:phase0-baseline:live:refresh:drift` chains refresh + drift checks for scheduled cadence runs.
+- `pnpm audit:phase0-baseline:live:drift` checks backend-scoped artifact freshness/drift gates (including optional reaction match/skip rate thresholds) and writes `phase0_baseline_live_backend_drift_<UTC-date>.md/.json`; `pnpm audit:phase0-baseline:live:refresh:drift` chains refresh + drift checks for scheduled cadence runs.
 - `pnpm audit:phase0-baseline:live:refresh:drift:rolling` performs the same chain using one UTC timestamp tag (`YYYY-MM-DD-HHMMSS`) across channel/gateway/backend/drift outputs so each cadence run preserves a distinct comparison point.
 - `pnpm audit:phase0-baseline:live:prune` (dry-run) and `pnpm audit:phase0-baseline:live:prune:apply` (delete) manage retention of rolling-tag artifacts to control artifact growth while preserving newest snapshots per family.
 - `pnpm audit:phase0-baseline:live:refresh:drift:rolling:prune` combines rolling refresh+drift with retention apply for one-command cron scheduling using a shared `TAG`; adjust retention depth with non-negative integer `KEEP_PER_FAMILY` and use generated `phase0_baseline_live_prune_<tag>.md/.json` artifacts for retention audit traceability.

docs/plans/2026-02-25-phase0-instrumentation-ticket-checklist.md

@@ -203,7 +203,7 @@ Phase 0 is complete when:
 2. A baseline summary artifact is generated and committed under `docs/plans/artifacts/`.
 3. No user-visible response behavior changed compared to pre-phase baseline.
 
-Follow-up status (2026-02-27): live channel-session artifacts exist under `docs/plans/artifacts/phase0_baseline_live_2026-02-27.*` via `pnpm audit:phase0-baseline:live` (anonymized IDs), and a second gateway-origin live window (including `run.cancel` + `cancel_requested`/`cancelled`) exists under `docs/plans/artifacts/phase0_baseline_live_gateway_2026-02-27.*`. Gateway window refreshes can now run via `pnpm audit:phase0-baseline:live:gateway` (auto-selected cancel window), all live windows can be refreshed together with `pnpm audit:phase0-baseline:live:refresh` (channel + gateway + backend-scoped `pi`/`native`; scheduling example included in README), backend artifact freshness/drift checks are now available via `pnpm audit:phase0-baseline:live:drift` (or chained with `pnpm audit:phase0-baseline:live:refresh:drift`) with drift report artifacts written to `docs/plans/artifacts/phase0_baseline_live_backend_drift_<tag>.{md,json}`, cadence runs can preserve distinct timestamped comparison points via `pnpm audit:phase0-baseline:live:refresh:drift:rolling` (supports shared `TAG` override), rolling-tag retention can be managed via `pnpm audit:phase0-baseline:live:prune` (dry-run) / `pnpm audit:phase0-baseline:live:prune:apply` with prune report artifacts written to `phase0_baseline_live_prune_<tag>.{md,json}` (and retained as a managed rolling family), and one-command cadence scheduling is available via `pnpm audit:phase0-baseline:live:refresh:drift:rolling:prune` (non-negative integer `KEEP_PER_FAMILY` optional override).
+Follow-up status (2026-02-27): live channel-session artifacts exist under `docs/plans/artifacts/phase0_baseline_live_2026-02-27.*` via `pnpm audit:phase0-baseline:live` (anonymized IDs), and a second gateway-origin live window (including `run.cancel` + `cancel_requested`/`cancelled`) exists under `docs/plans/artifacts/phase0_baseline_live_gateway_2026-02-27.*`. Gateway window refreshes can now run via `pnpm audit:phase0-baseline:live:gateway` (auto-selected cancel window), all live windows can be refreshed together with `pnpm audit:phase0-baseline:live:refresh` (channel + gateway + backend-scoped `pi`/`native`; scheduling example included in README), backend artifact freshness/drift checks are now available via `pnpm audit:phase0-baseline:live:drift` (or chained with `pnpm audit:phase0-baseline:live:refresh:drift`) with drift report artifacts written to `docs/plans/artifacts/phase0_baseline_live_backend_drift_<tag>.{md,json}` and optional reaction match/skip drift thresholds, cadence runs can preserve distinct timestamped comparison points via `pnpm audit:phase0-baseline:live:refresh:drift:rolling` (supports shared `TAG` override), rolling-tag retention can be managed via `pnpm audit:phase0-baseline:live:prune` (dry-run) / `pnpm audit:phase0-baseline:live:prune:apply` with prune report artifacts written to `phase0_baseline_live_prune_<tag>.{md,json}` (and retained as a managed rolling family), and one-command cadence scheduling is available via `pnpm audit:phase0-baseline:live:refresh:drift:rolling:prune` (non-negative integer `KEEP_PER_FAMILY` optional override).
 
 ## Subagent Model Assignment Plan
 

docs/plans/state.json

@@ -533,6 +533,25 @@
       ],
       "test_status": "pnpm test:run src/audit/phase0GatewayWindow.test.ts + pnpm typecheck passing"
     },
+    "phase0-live-baseline-drift-reaction-threshold-gates": {
+      "status": "completed",
+      "date": "2026-02-27",
+      "updated": "2026-02-27",
+      "summary": "Extended backend drift gating with optional reaction decision thresholds (`maxReactionMatchRateDropPp`, `maxReactionSkipRateIncreasePp`), wired new CLI flags, and enabled conservative defaults in package drift cadence commands.",
+      "files_modified": [
+        "src/audit/phase0BaselineDrift.ts",
+        "src/audit/phase0BaselineDrift.test.ts",
+        "scripts/check-phase0-baseline-backend-drift.ts",
+        "package.json",
+        "README.md",
+        "docs/api/PROTOCOL.md",
+        "docs/architecture/AGENT_DIAGRAM.md",
+        "docs/architecture/GATEWAY_SESSIONS_AND_QUEUE.md",
+        "docs/plans/2026-02-25-phase0-instrumentation-ticket-checklist.md",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm test:run src/audit/phase0BaselineDrift.test.ts + pnpm typecheck passing"
+    },
     "phase0-instrumentation-ticket-checklist": {
       "status": "completed",
       "date": "2026-02-25",

package.json

@@ -27,9 +27,9 @@
     "audit:phase0-baseline:live:native": "node --import tsx/esm scripts/capture-phase0-live-baseline.ts --audit ~/.local/share/flynn/audit.log --source channel --backend native --exclude-session-substring probe",
     "audit:phase0-baseline:live:gateway": "node --import tsx/esm scripts/capture-phase0-live-baseline.ts --audit ~/.local/share/flynn/audit.log --source gateway --auto-gateway-cancel-window",
     "audit:phase0-baseline:live:refresh": "pnpm audit:phase0-baseline:live && pnpm audit:phase0-baseline:live:gateway && pnpm audit:phase0-baseline:live:pi && pnpm audit:phase0-baseline:live:native",
-    "audit:phase0-baseline:live:drift": "node --import tsx/esm scripts/check-phase0-baseline-backend-drift.ts --artifacts-dir docs/plans/artifacts --backend pi_embedded,native --max-age-hours 36 --min-candidate-sampled-events 10 --max-sampled-events-drop-pct 80 --max-run-outcomes-drop-pct 80 --max-completion-rate-drop-pp 35 --max-cancel-rate-increase-pp 25 --max-error-rate-increase-pp 25 --max-cancel-latency-p95-increase-ms 6000 --write-default-artifacts",
+    "audit:phase0-baseline:live:drift": "node --import tsx/esm scripts/check-phase0-baseline-backend-drift.ts --artifacts-dir docs/plans/artifacts --backend pi_embedded,native --max-age-hours 36 --min-candidate-sampled-events 10 --max-sampled-events-drop-pct 80 --max-run-outcomes-drop-pct 80 --max-completion-rate-drop-pp 35 --max-cancel-rate-increase-pp 25 --max-error-rate-increase-pp 25 --max-cancel-latency-p95-increase-ms 6000 --max-reaction-match-rate-drop-pp 50 --max-reaction-skip-rate-increase-pp 50 --write-default-artifacts",
     "audit:phase0-baseline:live:refresh:drift": "pnpm audit:phase0-baseline:live:refresh && pnpm audit:phase0-baseline:live:drift",
-    "audit:phase0-baseline:live:refresh:drift:rolling": "TAG=${TAG:-$(date -u +%F-%H%M%S)} && node --import tsx/esm scripts/capture-phase0-live-baseline.ts --audit ~/.local/share/flynn/audit.log --source channel --exclude-session-substring probe --tag \"$TAG\" && node --import tsx/esm scripts/capture-phase0-live-baseline.ts --audit ~/.local/share/flynn/audit.log --source gateway --auto-gateway-cancel-window --tag \"$TAG\" && node --import tsx/esm scripts/capture-phase0-live-baseline.ts --audit ~/.local/share/flynn/audit.log --source channel --backend pi_embedded --exclude-session-substring probe --tag \"$TAG\" && node --import tsx/esm scripts/capture-phase0-live-baseline.ts --audit ~/.local/share/flynn/audit.log --source channel --backend native --exclude-session-substring probe --tag \"$TAG\" && node --import tsx/esm scripts/check-phase0-baseline-backend-drift.ts --artifacts-dir docs/plans/artifacts --backend pi_embedded,native --max-age-hours 36 --min-candidate-sampled-events 10 --max-sampled-events-drop-pct 80 --max-run-outcomes-drop-pct 80 --max-completion-rate-drop-pp 35 --max-cancel-rate-increase-pp 25 --max-error-rate-increase-pp 25 --max-cancel-latency-p95-increase-ms 6000 --write-default-artifacts --tag \"$TAG\" --report-tag \"$TAG\"",
+    "audit:phase0-baseline:live:refresh:drift:rolling": "TAG=${TAG:-$(date -u +%F-%H%M%S)} && node --import tsx/esm scripts/capture-phase0-live-baseline.ts --audit ~/.local/share/flynn/audit.log --source channel --exclude-session-substring probe --tag \"$TAG\" && node --import tsx/esm scripts/capture-phase0-live-baseline.ts --audit ~/.local/share/flynn/audit.log --source gateway --auto-gateway-cancel-window --tag \"$TAG\" && node --import tsx/esm scripts/capture-phase0-live-baseline.ts --audit ~/.local/share/flynn/audit.log --source channel --backend pi_embedded --exclude-session-substring probe --tag \"$TAG\" && node --import tsx/esm scripts/capture-phase0-live-baseline.ts --audit ~/.local/share/flynn/audit.log --source channel --backend native --exclude-session-substring probe --tag \"$TAG\" && node --import tsx/esm scripts/check-phase0-baseline-backend-drift.ts --artifacts-dir docs/plans/artifacts --backend pi_embedded,native --max-age-hours 36 --min-candidate-sampled-events 10 --max-sampled-events-drop-pct 80 --max-run-outcomes-drop-pct 80 --max-completion-rate-drop-pp 35 --max-cancel-rate-increase-pp 25 --max-error-rate-increase-pp 25 --max-cancel-latency-p95-increase-ms 6000 --max-reaction-match-rate-drop-pp 50 --max-reaction-skip-rate-increase-pp 50 --write-default-artifacts --tag \"$TAG\" --report-tag \"$TAG\"",
     "audit:phase0-baseline:live:prune": "KEEP_PER_FAMILY=${KEEP_PER_FAMILY:-8} && node --import tsx/esm scripts/prune-phase0-baseline-artifacts.ts --artifacts-dir docs/plans/artifacts --keep-per-family \"$KEEP_PER_FAMILY\" --write-default-artifacts",
     "audit:phase0-baseline:live:prune:apply": "KEEP_PER_FAMILY=${KEEP_PER_FAMILY:-8} && node --import tsx/esm scripts/prune-phase0-baseline-artifacts.ts --artifacts-dir docs/plans/artifacts --keep-per-family \"$KEEP_PER_FAMILY\" --apply --write-default-artifacts",
     "audit:phase0-baseline:live:refresh:drift:rolling:prune": "TAG=${TAG:-$(date -u +%F-%H%M%S)} && TAG=\"$TAG\" pnpm audit:phase0-baseline:live:refresh:drift:rolling && KEEP_PER_FAMILY=${KEEP_PER_FAMILY:-8} node --import tsx/esm scripts/prune-phase0-baseline-artifacts.ts --artifacts-dir docs/plans/artifacts --keep-per-family \"$KEEP_PER_FAMILY\" --apply --write-default-artifacts --report-tag \"$TAG\"",

scripts/check-phase0-baseline-backend-drift.ts

@@ -77,6 +77,8 @@ function usage(): string {
     '  --max-cancel-rate-increase-pp <number>',
     '  --max-error-rate-increase-pp <number>',
     '  --max-cancel-latency-p95-increase-ms <number>',
+    '  --max-reaction-match-rate-drop-pp <number>',
+    '  --max-reaction-skip-rate-increase-pp <number>',
   ].join('\n');
 }
 
@@ -184,6 +186,8 @@ function buildThresholds(values: Record<string, string | boolean | undefined>):
     maxCancelRateIncreasePp: parseOptionalNumber(values['max-cancel-rate-increase-pp'] as string | undefined, '--max-cancel-rate-increase-pp'),
     maxErrorRateIncreasePp: parseOptionalNumber(values['max-error-rate-increase-pp'] as string | undefined, '--max-error-rate-increase-pp'),
     maxCancelLatencyP95IncreaseMs: parseOptionalNumber(values['max-cancel-latency-p95-increase-ms'] as string | undefined, '--max-cancel-latency-p95-increase-ms'),
+    maxReactionMatchRateDropPp: parseOptionalNumber(values['max-reaction-match-rate-drop-pp'] as string | undefined, '--max-reaction-match-rate-drop-pp'),
+    maxReactionSkipRateIncreasePp: parseOptionalNumber(values['max-reaction-skip-rate-increase-pp'] as string | undefined, '--max-reaction-skip-rate-increase-pp'),
   };
 }
 
@@ -345,6 +349,8 @@ async function main(): Promise<void> {
       'max-cancel-rate-increase-pp': { type: 'string' },
       'max-error-rate-increase-pp': { type: 'string' },
       'max-cancel-latency-p95-increase-ms': { type: 'string' },
+      'max-reaction-match-rate-drop-pp': { type: 'string' },
+      'max-reaction-skip-rate-increase-pp': { type: 'string' },
       format: { type: 'string' },
       out: { type: 'string' },
       help: { type: 'boolean', short: 'h' },

src/audit/phase0BaselineDrift.test.ts

@@ -381,6 +381,12 @@ describe('phase0BaselineDrift', () => {
     expect(() => evaluatePhase0BaselineDriftGate(comparison, {
       minCandidateSampledEvents: -5,
     })).toThrow('minCandidateSampledEvents');
+    expect(() => evaluatePhase0BaselineDriftGate(comparison, {
+      maxReactionMatchRateDropPp: -1,
+    })).toThrow('maxReactionMatchRateDropPp');
+    expect(() => evaluatePhase0BaselineDriftGate(comparison, {
+      maxReactionSkipRateIncreasePp: -1,
+    })).toThrow('maxReactionSkipRateIncreasePp');
   });
 
   it('rejects non-integer sampled-event minimum thresholds', () => {
@@ -427,4 +433,95 @@ describe('phase0BaselineDrift', () => {
       minBaselineSampledEvents: 8.2,
     })).toThrow('minBaselineSampledEvents');
   });
+
+  it('evaluates optional reaction rate drift thresholds', () => {
+    const comparison = comparePhase0BaselineDrift(
+      {
+        sampled_event_count: 50,
+        summary: {
+          event_counts: {
+            run_state: 0,
+            run_cancel: 0,
+            reaction_match: 0,
+            reaction_skip: 0,
+          },
+          run_outcomes: {
+            overall: {
+              total_outcomes: 20,
+              complete: 18,
+              cancelled: 1,
+              error: 1,
+              cancel_requested: 0,
+              start: 20,
+              completion_rate_pct: 90,
+              cancel_rate_pct: 5,
+              error_rate_pct: 5,
+            },
+            by_channel: [],
+            by_session: [],
+          },
+          cancel_latency_ms: null,
+          reactions: {
+            matched: 4,
+            skipped: 6,
+            total: 10,
+            match_rate_pct: 40,
+            skip_rate_pct: 60,
+            skip_reasons: [],
+          },
+        },
+      },
+      {
+        sampled_event_count: 50,
+        summary: {
+          event_counts: {
+            run_state: 0,
+            run_cancel: 0,
+            reaction_match: 0,
+            reaction_skip: 0,
+          },
+          run_outcomes: {
+            overall: {
+              total_outcomes: 20,
+              complete: 18,
+              cancelled: 1,
+              error: 1,
+              cancel_requested: 0,
+              start: 20,
+              completion_rate_pct: 90,
+              cancel_rate_pct: 5,
+              error_rate_pct: 5,
+            },
+            by_channel: [],
+            by_session: [],
+          },
+          cancel_latency_ms: null,
+          reactions: {
+            matched: 7,
+            skipped: 3,
+            total: 10,
+            match_rate_pct: 70,
+            skip_rate_pct: 30,
+            skip_reasons: [],
+          },
+        },
+      },
+    );
+
+    const pass = evaluatePhase0BaselineDriftGate(comparison, {
+      maxReactionMatchRateDropPp: 35,
+      maxReactionSkipRateIncreasePp: 35,
+    });
+    expect(pass.pass).toBe(true);
+
+    const fail = evaluatePhase0BaselineDriftGate(comparison, {
+      maxReactionMatchRateDropPp: 20,
+      maxReactionSkipRateIncreasePp: 20,
+    });
+    expect(fail.pass).toBe(false);
+    expect(fail.criteria.filter((row) => !row.pass).map((row) => row.criterion)).toEqual([
+      'reaction_match_rate_drop_pp',
+      'reaction_skip_rate_increase_pp',
+    ]);
+  });
 });

src/audit/phase0BaselineDrift.ts

@@ -46,6 +46,8 @@ export interface Phase0BaselineDriftGateThresholds {
   maxCancelRateIncreasePp?: number;
   maxErrorRateIncreasePp?: number;
   maxCancelLatencyP95IncreaseMs?: number;
+  maxReactionMatchRateDropPp?: number;
+  maxReactionSkipRateIncreasePp?: number;
 }
 
 export interface Phase0BaselineDriftGateCriterion {
@@ -332,6 +334,48 @@ export function evaluatePhase0BaselineDriftGate(
     }
   }
 
+  const maxReactionMatchRateDropPp = readThreshold(thresholds.maxReactionMatchRateDropPp, 'maxReactionMatchRateDropPp');
+  if (typeof maxReactionMatchRateDropPp === 'number') {
+    const delta = comparison.deltas.reaction_match_rate_pp;
+    if (delta === null) {
+      criteria.push({
+        criterion: 'reaction_match_rate_drop_pp',
+        pass: !requireBaselineHistory,
+        actual: 'n/a',
+        threshold: `<= ${maxReactionMatchRateDropPp}`,
+      });
+    } else {
+      const drop = Math.max(0, -delta);
+      criteria.push({
+        criterion: 'reaction_match_rate_drop_pp',
+        pass: drop <= maxReactionMatchRateDropPp,
+        actual: `${Math.round(drop * 100) / 100}`,
+        threshold: `<= ${maxReactionMatchRateDropPp}`,
+      });
+    }
+  }
+
+  const maxReactionSkipRateIncreasePp = readThreshold(thresholds.maxReactionSkipRateIncreasePp, 'maxReactionSkipRateIncreasePp');
+  if (typeof maxReactionSkipRateIncreasePp === 'number') {
+    const delta = comparison.deltas.reaction_skip_rate_pp;
+    if (delta === null) {
+      criteria.push({
+        criterion: 'reaction_skip_rate_increase_pp',
+        pass: !requireBaselineHistory,
+        actual: 'n/a',
+        threshold: `<= ${maxReactionSkipRateIncreasePp}`,
+      });
+    } else {
+      const increase = Math.max(0, delta);
+      criteria.push({
+        criterion: 'reaction_skip_rate_increase_pp',
+        pass: increase <= maxReactionSkipRateIncreasePp,
+        actual: `${Math.round(increase * 100) / 100}`,
+        threshold: `<= ${maxReactionSkipRateIncreasePp}`,
+      });
+    }
+  }
+
   return {
     pass: criteria.every((row) => row.pass),
     criteria,