fix(audit): validate phase0 artifact tag inputs

Add shared artifact-tag normalization/validation and apply it to capture, drift, and prune scripts for --tag/--report-tag/--baseline-tag paths. Architecture diagrams reviewed; no flow changes required.

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}` 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).
+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 with filename-safe tag values), 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

@@ -552,6 +552,24 @@
       ],
       "test_status": "pnpm test:run src/audit/phase0BaselineDrift.test.ts + pnpm typecheck passing"
     },
+    "phase0-live-baseline-artifact-tag-validation-hardening": {
+      "status": "completed",
+      "date": "2026-02-27",
+      "updated": "2026-02-27",
+      "summary": "Added shared artifact-tag normalization/validation and applied it across phase-0 capture, drift, and prune scripts (`--tag`, `--report-tag`, `--baseline-tag`) to enforce filename-safe tags and block malformed path-like values.",
+      "files_modified": [
+        "src/audit/artifactTag.ts",
+        "src/audit/artifactTag.test.ts",
+        "scripts/capture-phase0-live-baseline.ts",
+        "scripts/check-phase0-baseline-backend-drift.ts",
+        "scripts/prune-phase0-baseline-artifacts.ts",
+        "README.md",
+        "docs/api/PROTOCOL.md",
+        "docs/plans/2026-02-25-phase0-instrumentation-ticket-checklist.md",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm test:run src/audit/artifactTag.test.ts src/audit/phase0BaselineDrift.test.ts + pnpm typecheck passing"
+    },
     "phase0-instrumentation-ticket-checklist": {
       "status": "completed",
       "date": "2026-02-25",