diff --git a/NEXT_AGENT_NOTES.md b/NEXT_AGENT_NOTES.md
index f227893..ca40c02 100644
--- a/NEXT_AGENT_NOTES.md
+++ b/NEXT_AGENT_NOTES.md
@@ -2,6 +2,11 @@
 
 ## Current Canonical State (2026-02-26)
 
+- `TEST_ONLY` artifact rule:
+  - Any path under `logs/taskitem_runs/TEST_ONLY_*` is validation-only data.
+  - Do not use hardened specs in `TEST_ONLY_*` as source-of-truth project specs.
+  - See `logs/taskitem_runs/TEST_ONLY_README_2026-02-26.md`.
+
 - Read first:
   - `docs/progress_log_2026-02-26.md`
   - `docs/generator_readiness_gap_registry_2026-02-26.md`
diff --git a/docs/constructive_editing_runtime_plan.md b/docs/constructive_editing_runtime_plan.md
index e6e0b89..09b88c8 100644
--- a/docs/constructive_editing_runtime_plan.md
+++ b/docs/constructive_editing_runtime_plan.md
@@ -146,5 +146,5 @@ Start Phase A:
 Parallel planning tranche (active):
 - `sprint228_plan.md` to `sprint231_plan.md`
 - baseline artifacts:
-  - `logs/taskitem_runs/spec_planning_baseline_20260226/fullstack_spec_readiness.json`
-  - `logs/taskitem_runs/spec_planning_baseline_20260226/deterministic_spec_readiness.json`
+  - `logs/taskitem_runs/TEST_ONLY_spec_planning_baseline_20260226/fullstack_spec_readiness.json`
+  - `logs/taskitem_runs/TEST_ONLY_spec_planning_baseline_20260226/deterministic_spec_readiness.json`
diff --git a/docs/progress_log_2026-02-26.md b/docs/progress_log_2026-02-26.md
index 3fb7820..d71b44c 100644
--- a/docs/progress_log_2026-02-26.md
+++ b/docs/progress_log_2026-02-26.md
@@ -72,3 +72,6 @@
   - example product meta specs (10)
 - Batch report:
   - `docs/spec_hardening_batch_report_2026-02-26.md`
+- Artifact isolation update:
+  - moved planning/hardening outputs to `logs/taskitem_runs/TEST_ONLY_*` paths.
+  - wrapper default now writes to `TEST_ONLY_spec_hardening_gate_*`.
diff --git a/docs/spec_hardening_batch_report_2026-02-26.md b/docs/spec_hardening_batch_report_2026-02-26.md
index d8dc45d..db433b1 100644
--- a/docs/spec_hardening_batch_report_2026-02-26.md
+++ b/docs/spec_hardening_batch_report_2026-02-26.md
@@ -12,13 +12,13 @@ Corpora:
 ## Batch Artifacts
 
 Drive batch:
-- `logs/taskitem_runs/drive_spec_hardening_batch_20260226/results.jsonl`
-- `logs/taskitem_runs/drive_spec_hardening_batch_20260226/summary.json`
-- `logs/taskitem_runs/drive_spec_hardening_batch_20260226/quality_summary.json`
+- `logs/taskitem_runs/TEST_ONLY_drive_spec_hardening_batch_20260226/results.jsonl`
+- `logs/taskitem_runs/TEST_ONLY_drive_spec_hardening_batch_20260226/summary.json`
+- `logs/taskitem_runs/TEST_ONLY_drive_spec_hardening_batch_20260226/quality_summary.json`
 
 Example project meta batch:
-- `logs/taskitem_runs/example_projectmeta_hardening_batch_20260226/results.jsonl`
-- `logs/taskitem_runs/example_projectmeta_hardening_batch_20260226/summary.json`
+- `logs/taskitem_runs/TEST_ONLY_example_projectmeta_hardening_batch_20260226/results.jsonl`
+- `logs/taskitem_runs/TEST_ONLY_example_projectmeta_hardening_batch_20260226/summary.json`
 
 ## High-Density Outcomes
 
diff --git a/docs/spec_planning_baseline_2026-02-26.md b/docs/spec_planning_baseline_2026-02-26.md
index 8dfee45..5d11b38 100644
--- a/docs/spec_planning_baseline_2026-02-26.md
+++ b/docs/spec_planning_baseline_2026-02-26.md
@@ -1,8 +1,8 @@
 # Spec Planning Baseline - 2026-02-26
 
 Run artifacts:
-- `logs/taskitem_runs/spec_planning_baseline_20260226/fullstack_spec_readiness.json`
-- `logs/taskitem_runs/spec_planning_baseline_20260226/deterministic_spec_readiness.json`
+- `logs/taskitem_runs/TEST_ONLY_spec_planning_baseline_20260226/fullstack_spec_readiness.json`
+- `logs/taskitem_runs/TEST_ONLY_spec_planning_baseline_20260226/deterministic_spec_readiness.json`
 
 ## Results
 
diff --git a/docs/sprint228_231_execution_tracker_2026-02-26.md b/docs/sprint228_231_execution_tracker_2026-02-26.md
index 46f2e10..5764c4d 100644
--- a/docs/sprint228_231_execution_tracker_2026-02-26.md
+++ b/docs/sprint228_231_execution_tracker_2026-02-26.md
@@ -25,12 +25,12 @@ Planned and started:
 
 ## Baseline Evidence
 
-- `logs/taskitem_runs/spec_planning_baseline_20260226/fullstack_spec_readiness.json`
-- `logs/taskitem_runs/spec_planning_baseline_20260226/deterministic_spec_readiness.json`
-- `logs/taskitem_runs/spec_planning_hardening_20260226/sprint228_before.json`
-- `logs/taskitem_runs/spec_planning_hardening_20260226/sprint228_after.json`
-- `logs/taskitem_runs/spec_planning_hardening_20260226/sprint228_hardened.md`
-- `logs/taskitem_runs/spec_hardening_gate_20260226_s228_r2/report.json`
+- `logs/taskitem_runs/TEST_ONLY_spec_planning_baseline_20260226/fullstack_spec_readiness.json`
+- `logs/taskitem_runs/TEST_ONLY_spec_planning_baseline_20260226/deterministic_spec_readiness.json`
+- `logs/taskitem_runs/TEST_ONLY_spec_planning_hardening_20260226/sprint228_before.json`
+- `logs/taskitem_runs/TEST_ONLY_spec_planning_hardening_20260226/sprint228_after.json`
+- `logs/taskitem_runs/TEST_ONLY_spec_planning_hardening_20260226/sprint228_hardened.md`
+- `logs/taskitem_runs/TEST_ONLY_spec_hardening_gate_20260226_s228_r2/report.json`
 
 Observed baseline:
 - both sample docs currently return `needs_spec_hardening`
@@ -49,7 +49,7 @@ Pipeline hard-gate proof:
 Reusable flow wrapper:
 - `tools/mcp/run_spec_hardening_gate.sh`
 - example invocation:
-  - `tools/mcp/run_spec_hardening_gate.sh sprint228_plan.md logs/taskitem_runs/spec_hardening_gate_20260226_s228_r2`
+  - `tools/mcp/run_spec_hardening_gate.sh sprint228_plan.md logs/taskitem_runs/TEST_ONLY_spec_hardening_gate_20260226_s228_r2`
 
 ## Explicit Completion Signal
 
diff --git a/docs/stale_log_manifest_2026-02-26.md b/docs/stale_log_manifest_2026-02-26.md
index e1512ee..ecabe52 100644
--- a/docs/stale_log_manifest_2026-02-26.md
+++ b/docs/stale_log_manifest_2026-02-26.md
@@ -29,3 +29,8 @@ These are useful for history but should not be treated as current execution trut
 ## Rule For Next Agents
 
 When docs disagree, trust newest dated execution tracker + run artifacts under `logs/taskitem_runs/`.
+
+## Test-Only Artifact Rule
+
+- Treat directories under `logs/taskitem_runs/TEST_ONLY_*` as validation artifacts only.
+- Never treat markdown specs generated within `TEST_ONLY_*` directories as authoritative product specs.
diff --git a/tools/mcp/run_spec_hardening_gate.sh b/tools/mcp/run_spec_hardening_gate.sh
index 3e76d38..3ab23ae 100755
--- a/tools/mcp/run_spec_hardening_gate.sh
+++ b/tools/mcp/run_spec_hardening_gate.sh
@@ -3,7 +3,7 @@ set -euo pipefail
 
 ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
 SPEC_INPUT="${1:?usage: run_spec_hardening_gate.sh <spec.md> [out_dir]}"
-OUT_DIR="${2:-$ROOT_DIR/logs/taskitem_runs/spec_hardening_gate_$(date +%Y%m%d_%H%M%S)}"
+OUT_DIR="${2:-$ROOT_DIR/logs/taskitem_runs/TEST_ONLY_spec_hardening_gate_$(date +%Y%m%d_%H%M%S)}"
 MIN_SCORE="${WSTONE_SPEC_READINESS_MIN_SCORE:-65}"
 RUN_PIPELINE="${WSTONE_SPEC_HARDENING_RUN_PIPELINE:-1}"