diff --git a/.github/workflows/harness-coauthor-guard.yml b/.github/workflows/harness-coauthor-guard.yml
index 63b347d12d..f47e899332 100644
--- a/.github/workflows/harness-coauthor-guard.yml
+++ b/.github/workflows/harness-coauthor-guard.yml
@@ -91,17 +91,21 @@ jobs:
       # Per the c.1331+107-L2 lesson, the script always exits 0 here on a
       # clean working tree; we capture findings via JSON, not exit code, to
       # distinguish "0 findings" from "detector crashed".
+      # NOTE (collision /tmp, 2026-09-28) : chemins en `${{ runner.temp }}` (per-slot)
+      # au lieu de `/tmp` nu -- `/tmp` est hote-global sur le runner a slots
+      # partages, et pip/solution-leak-guard y ecrivaient les memes noms au
+      # format LISTE (cf pip-leak-guard.yml, #18059).
       - name: HEAD scan
         id: head_scan
         run: |
-          python scripts/notebook_tools/check_harness_coauthor.py --json > /tmp/head.json
+          python scripts/notebook_tools/check_harness_coauthor.py --json > "${{ runner.temp }}/coauthor-head.json"
           rc=$?
           if [ "$rc" -ne 0 ] && [ "$rc" -ne 1 ]; then
             echo "::error title=Detector crashed::check_harness_coauthor.py exited with non-standard code $rc. The gate cannot be trusted -- investigate before merging."
             exit 1
           fi
-          HEAD_VERDICT=$(python -c "import json; print(json.load(open('/tmp/head.json'))['verdict'])")
-          HEAD_TOTAL=$(python -c "import json; print(json.load(open('/tmp/head.json'))['total_findings'])")
+          HEAD_VERDICT=$(python -c "import json; print(json.load(open('${{ runner.temp }}/coauthor-head.json'))['verdict'])")
+          HEAD_TOTAL=$(python -c "import json; print(json.load(open('${{ runner.temp }}/coauthor-head.json'))['total_findings'])")
           echo "head_verdict=$HEAD_VERDICT" >> "$GITHUB_OUTPUT"
           echo "head_total=$HEAD_TOTAL" >> "$GITHUB_OUTPUT"
           echo "HEAD verdict: $HEAD_VERDICT ($HEAD_TOTAL findings)"
@@ -124,7 +128,7 @@ jobs:
       - name: BASE scan
         if: github.event_name == 'pull_request'
         run: |
-          python scripts/notebook_tools/check_harness_coauthor.py --json --repo-root _base > /tmp/base.json || true
+          python scripts/notebook_tools/check_harness_coauthor.py --json --repo-root _base > "${{ runner.temp }}/coauthor-base.json" || true
 
       # DELTA check: a NEW finding introduced by the PR fails the gate.
       # Inherited findings (post-Phase-1 main = 0) are tolerated, mirroring
@@ -139,8 +143,8 @@ jobs:
           import json
           import sys
 
-          base = json.load(open("/tmp/base.json"))
-          head = json.load(open("/tmp/head.json"))
+          base = json.load(open("${{ runner.temp }}/coauthor-base.json"))
+          head = json.load(open("${{ runner.temp }}/coauthor-head.json"))
 
           base_keys = {(f["file"], f["line"], f["match"]) for f in base["findings"]}
           head_keys = {(f["file"], f["line"], f["match"]) for f in head["findings"]}
diff --git a/.github/workflows/pip-leak-guard.yml b/.github/workflows/pip-leak-guard.yml
index 15abe401ad..ebfbe9fbf9 100644
--- a/.github/workflows/pip-leak-guard.yml
+++ b/.github/workflows/pip-leak-guard.yml
@@ -50,10 +50,19 @@ jobs:
         with:
           python-version: '3.11'
 
+      # NOTE (collision /tmp, 2026-09-28) : les chemins de travail passent par
+      # `${{ runner.temp }}` (per-slot/per-job), jamais `/tmp` nu. `/tmp` est
+      # hote-global sur le runner a slots partages : `harness-coauthor-guard.yml`
+      # et `solution-leak-guard.yml` y ecrivaient AUSSI `/tmp/head.json`, mais au
+      # format DICT -- un job parallele lisait le fichier d'un autre et
+      # `pip_leak_delta.py` crashait (`'str' object has no attribute 'get'`,
+      # measure sur #18059, job 109030466607). Un prefixe par workflow ne
+      # suffirait pas (deux PRs du meme workflow sur deux slots collisionnent) :
+      # runner.temp est la seule borne per-job.
       - name: HEAD scan (PR head)
         run: |
           python scripts/notebook_tools/audit_pip_install_cells.py --scan-all
-          python scripts/notebook_tools/audit_pip_install_cells.py --scan-all --json > /tmp/head.json
+          python scripts/notebook_tools/audit_pip_install_cells.py --scan-all --json > "${{ runner.temp }}/pip-head.json"
 
       # Swap MyIA.AI.Notebooks/ to the PR base ref, scan, then restore. head.json
       # is already captured above, so the swap cannot contaminate the delta.
@@ -66,9 +75,9 @@ jobs:
           # (le working tree est restore depuis ce checkout juste apres).
           git fetch --depth=1 origin "${{ github.event.pull_request.base.sha }}" -q
           git checkout ${{ github.event.pull_request.base.sha }} -- MyIA.AI.Notebooks
-          python scripts/notebook_tools/audit_pip_install_cells.py --scan-all --json > /tmp/base.json
+          python scripts/notebook_tools/audit_pip_install_cells.py --scan-all --json > "${{ runner.temp }}/pip-base.json"
           git checkout HEAD -- MyIA.AI.Notebooks
 
       - name: "Fail if HIGH delta > 0 (new !pip install leaks introduced)"
         if: github.event_name == 'pull_request'
-        run: python scripts/notebook_tools/pip_leak_delta.py /tmp/base.json /tmp/head.json
+        run: python scripts/notebook_tools/pip_leak_delta.py "${{ runner.temp }}/pip-base.json" "${{ runner.temp }}/pip-head.json"
diff --git a/.github/workflows/solution-leak-guard.yml b/.github/workflows/solution-leak-guard.yml
index f4ff5e4582..c0b28ea3d1 100644
--- a/.github/workflows/solution-leak-guard.yml
+++ b/.github/workflows/solution-leak-guard.yml
@@ -84,9 +84,13 @@ jobs:
         with:
           python-version: '3.11'
 
+      # NOTE (collision /tmp, 2026-09-28) : `${{ runner.temp }}` (per-slot)
+      # au lieu de `/tmp` nu -- `/tmp` est hote-global sur le runner a slots
+      # partages et `harness-coauthor-guard.yml` y ecrivait le meme
+      # `/tmp/head.json` au format dict (cf pip-leak-guard.yml, #18059).
       - name: HEAD scan (PR head)
         run: |
-          python scripts/notebook_tools/audit_solution_leaks.py --json > /tmp/head.json
+          python scripts/notebook_tools/audit_solution_leaks.py --json > "${{ runner.temp }}/solution-head.json"
 
       # Swap MyIA.AI.Notebooks/ to the PR base ref, scan, then restore. head.json
       # is already captured above, so the swap cannot contaminate the delta.
@@ -99,7 +103,7 @@ jobs:
           # (le working tree est restore depuis ce checkout juste apres).
           git fetch --depth=1 origin "${{ github.event.pull_request.base.sha }}" -q
           git checkout ${{ github.event.pull_request.base.sha }} -- MyIA.AI.Notebooks
-          python scripts/notebook_tools/audit_solution_leaks.py --json > /tmp/base.json
+          python scripts/notebook_tools/audit_solution_leaks.py --json > "${{ runner.temp }}/solution-base.json"
           git checkout HEAD -- MyIA.AI.Notebooks
 
       - name: "Report HIGH delta (WARN — never fails)"
@@ -113,7 +117,7 @@ jobs:
             echo "Detector candidates, not auto-verdicts: verify by CONTENT"
             echo "(cf exercise-example-labeling.md) — a guided example is legitimate._"
             echo ""
-            python scripts/notebook_tools/solution_leak_delta.py /tmp/base.json /tmp/head.json
+            python scripts/notebook_tools/solution_leak_delta.py "${{ runner.temp }}/solution-base.json" "${{ runner.temp }}/solution-head.json"
           } >> "$GITHUB_STEP_SUMMARY"
 
       # workflow_dispatch (no base ref): single scan, full markdown report to summary.