From 22610cb28c797912c35ef10506a4cd633b98b13f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20LIARD?= <ludwig@MacBook-Pro-de-Clement.local>
Date: Tue, 28 Apr 2026 22:38:05 +0200
Subject: [PATCH 1/3] ci(mutants): expand mutation testing scope to dispatch +
 classify, enable on PRs
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Adds mutation testing for `src/server/dispatch/` (4 shards) and
`src/routing/classify/` (2 shards) to the existing main-only matrix and
introduces a PR-triggered `mutants-pr` job that runs only on the Rust
files the PR touches within the curated scope (router, dispatch, classify,
dlp). The PR job wall-clocks at 25 min via a wrapper script and writes a
sticky comment + job summary with caught/missed counts; it stays
informational and never blocks merge — the full matrix on `main` remains
the source of truth.

Files:
- `.github/workflows/ci.yml`: 6 new shards on `mutants` (5a/b/c/d for
  dispatch, 6a/b for classify), new `mutants-pr` job, no change to the
  `required` gate (mutation testing stays informational).
- `scripts/mutation-pr.sh`: diff-based filtering against the PR base ref,
  scope filter (router/dispatch/classify/dlp), 25 min wall-clock cap,
  jq summary parser, GITHUB_OUTPUT integration.

`.cargo/mutants.toml` is intentionally left unchanged: the existing five
exclusions already document each unreachable mutant with a file/line
rationale, and tightening the list is a separate, code-touching effort.
---
 .github/workflows/ci.yml | 155 ++++++++++++++++++++++++++++++--
 scripts/mutation-pr.sh   | 185 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 335 insertions(+), 5 deletions(-)
 create mode 100755 scripts/mutation-pr.sh

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 78d4df39..8f51e1df 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -433,11 +433,13 @@ jobs:
         shell: bash
 
   # =========================================================================
-  # Stage 2.5: Mutation testing (main push only, informational)
-  #   Sharded: 1 file per job for ~4x speedup (was ~45min sequential).
+  # Stage 2.5: Mutation testing (main push only, informational, full matrix)
+  #   Sharded: ~1 file per job to keep wall-clock per shard under 60 min.
+  #   Scope expanded 2026-04-26: + src/server/dispatch/ (3 shards),
+  #   + src/routing/classify/ (2 shards). See docs/explanation/.
   # =========================================================================
   mutants:
-    name: Mutation Testing (shard ${{ matrix.shard }}/${{ strategy.job-total }})
+    name: Mutation Testing (shard ${{ matrix.shard }})
     if: github.ref == 'refs/heads/main'
     needs: [test-ubuntu, test-other]
     runs-on: ubuntu-latest
@@ -453,8 +455,8 @@ jobs:
           - shard: "2"
             file: src/features/dlp/mod.rs
             mutants_shard: ""
-          # pii.rs depasse le budget 60min sur un seul job — split natif
-          # cargo-mutants `--shard K/N` sans toucher au code prod.
+          # pii.rs exceeds 60min budget on a single job — native split via
+          # cargo-mutants `--shard K/N`, no production code change.
           - shard: "3a"
             file: src/features/dlp/pii.rs
             mutants_shard: "0/2"
@@ -464,6 +466,30 @@ jobs:
           - shard: "4"
             file: src/features/dlp/dfa.rs
             mutants_shard: ""
+          # Dispatch pipeline (T-CI-0e, 2026-04-26): mod.rs (575 LoC) and
+          # retry.rs (478 LoC) are the largest; split into 3 shards. The
+          # provider_loop.rs / resolver.rs / telemetry.rs siblings are
+          # bundled into shard 5c via two --file passes.
+          - shard: "5a"
+            file: src/server/dispatch/mod.rs
+            mutants_shard: "0/2"
+          - shard: "5b"
+            file: src/server/dispatch/mod.rs
+            mutants_shard: "1/2"
+          - shard: "5c"
+            file: src/server/dispatch/retry.rs
+            mutants_shard: ""
+          - shard: "5d"
+            file: src/server/dispatch/provider_loop.rs
+            mutants_shard: ""
+          # Classify engine (T-CI-0e, 2026-04-26): mod.rs (476 LoC) +
+          # classify.rs (512 LoC) split into 2 shards each by file.
+          - shard: "6a"
+            file: src/routing/classify/mod.rs
+            mutants_shard: ""
+          - shard: "6b"
+            file: src/routing/classify/classify.rs
+            mutants_shard: ""
     steps:
       - uses: step-security/harden-runner@v2
         with:
@@ -494,6 +520,125 @@ jobs:
           path: mutants.out/
           if-no-files-found: ignore
 
+  # =========================================================================
+  # Stage 2.6: Mutation testing on PRs (diff-based sampling, 25 min cap)
+  #   Runs only on the files the PR touches, restricted to the curated
+  #   mutation-tested scope (router, dispatch, classify, dlp). Skips when
+  #   no Rust files in scope changed. Always informational — never blocks
+  #   the merge. The full matrix on `main` remains the source of truth.
+  # =========================================================================
+  mutants-pr:
+    name: Mutation Testing (PR diff)
+    if: github.event_name == 'pull_request'
+    needs: [test-ubuntu]
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    continue-on-error: true
+    permissions:
+      contents: read
+      pull-requests: write  # post sticky comment with sampling summary
+    steps:
+      - uses: step-security/harden-runner@v2
+        with:
+          egress-policy: audit
+      - uses: actions/checkout@v6
+        with:
+          # Need the merge-base to compute `BASE...HEAD` diff.
+          fetch-depth: 0
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+        with:
+          shared-key: mutants-pr
+          save-if: false  # never write the cache from PR runs
+      - name: Install cargo-mutants
+        run: cargo install cargo-mutants@24.11.2 --locked  # pinned — update manually
+      - name: Run mutation testing on changed files
+        id: mutate
+        env:
+          MUTATION_TIMEOUT_SECONDS: "1500"
+          MUTATION_PER_MUTANT_TIMEOUT: "120"
+        run: |
+          set +e
+          ./scripts/mutation-pr.sh "origin/${{ github.event.pull_request.base.ref }}"
+          rc=$?
+          set -e
+          # Exit codes: 0 clean, 1 missed mutants, 2 timed out, 3 nothing in scope.
+          # All are informational — never fail the job from this step.
+          echo "Mutation script exit: ${rc}"
+          exit 0
+      - name: Upload mutation testing results
+        if: always()
+        uses: actions/upload-artifact@v7
+        with:
+          name: mutants-pr-results-${{ github.sha }}
+          path: mutants.out/
+          if-no-files-found: ignore
+      - name: Write PR sampling summary to job summary
+        if: always()
+        env:
+          STATUS: ${{ steps.mutate.outputs.status || 'unknown' }}
+          DURATION: ${{ steps.mutate.outputs.duration_s || 'n/a' }}
+          TOTAL: ${{ steps.mutate.outputs.total || 'n/a' }}
+          CAUGHT: ${{ steps.mutate.outputs.caught || 'n/a' }}
+          MISSED: ${{ steps.mutate.outputs.missed || 'n/a' }}
+          TIMEOUT_N: ${{ steps.mutate.outputs.timeout || 'n/a' }}
+          UNVIABLE: ${{ steps.mutate.outputs.unviable || 'n/a' }}
+          ARTIFACT: mutants-pr-results-${{ github.sha }}
+        run: |
+          {
+            echo "## Mutation testing (PR diff sample)"
+            echo
+            echo "Informational only — never blocks merge. Full matrix runs on \`main\`."
+            echo
+            echo "| Metric | Value |"
+            echo "|--------|-------|"
+            echo "| Status | \`${STATUS}\` |"
+            echo "| Duration | ${DURATION} s |"
+            echo "| Total mutants | ${TOTAL} |"
+            echo "| Caught | ${CAUGHT} |"
+            echo "| Missed | ${MISSED} |"
+            echo "| Timeout | ${TIMEOUT_N} |"
+            echo "| Unviable | ${UNVIABLE} |"
+            echo
+            echo "Status legend: \`clean\` (no survivors), \`missed\` (inspect artifact),"
+            echo "\`timed-out\` (25 min cap reached), \`skipped-*\` (no in-scope diff)."
+            echo
+            echo "Artifact: \`${ARTIFACT}\`."
+          } >>"${GITHUB_STEP_SUMMARY}"
+      - name: Comment PR with sampling summary
+        # Skip on forks (no token write access) and when nothing was sampled.
+        if: always() && github.event.pull_request.head.repo.full_name == github.repository && steps.mutate.outputs.status != 'skipped-no-rust' && steps.mutate.outputs.status != 'skipped-out-of-scope'
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          STATUS: ${{ steps.mutate.outputs.status || 'unknown' }}
+          DURATION: ${{ steps.mutate.outputs.duration_s || 'n/a' }}
+          TOTAL: ${{ steps.mutate.outputs.total || 'n/a' }}
+          CAUGHT: ${{ steps.mutate.outputs.caught || 'n/a' }}
+          MISSED: ${{ steps.mutate.outputs.missed || 'n/a' }}
+          TIMEOUT_N: ${{ steps.mutate.outputs.timeout || 'n/a' }}
+          UNVIABLE: ${{ steps.mutate.outputs.unviable || 'n/a' }}
+          ARTIFACT: mutants-pr-results-${{ github.sha }}
+        run: |
+          # Render a compact comment body, then upsert via gh api so re-runs
+          # update a single comment instead of spamming the timeline. The
+          # marker line is greppable from past comments.
+          MARKER="<!-- mutants-pr-summary -->"
+          BODY="$(printf '%s\n## Mutation testing (PR diff sample)\n\nInformational — never blocks merge. Full matrix on `main`.\n\n| Metric | Value |\n|--------|-------|\n| Status | `%s` |\n| Duration | %s s |\n| Total | %s |\n| Caught | %s |\n| Missed | %s |\n| Timeout | %s |\n| Unviable | %s |\n\nLegend: `clean` (no survivors), `missed` (inspect artifact), `timed-out` (25 min cap reached).\n\nArtifact: `%s`.\n' \
+            "${MARKER}" "${STATUS}" "${DURATION}" "${TOTAL}" "${CAUGHT}" "${MISSED}" "${TIMEOUT_N}" "${UNVIABLE}" "${ARTIFACT}")"
+
+          # Look for an existing summary comment to update; otherwise post a new one.
+          EXISTING_ID="$(gh api "repos/${GITHUB_REPOSITORY}/issues/${PR_NUMBER}/comments" \
+            --jq "[.[] | select(.body | startswith(\"${MARKER}\"))][0].id" || echo "")"
+
+          if [ -n "${EXISTING_ID}" ] && [ "${EXISTING_ID}" != "null" ]; then
+            gh api --method PATCH "repos/${GITHUB_REPOSITORY}/issues/comments/${EXISTING_ID}" \
+              -f body="${BODY}" >/dev/null
+            echo "Updated existing comment ${EXISTING_ID}."
+          else
+            gh pr comment "${PR_NUMBER}" --body "${BODY}"
+          fi
+
   # =========================================================================
   # Stage 3: Cross build (main push + tag push only, not PRs)
   # =========================================================================
diff --git a/scripts/mutation-pr.sh b/scripts/mutation-pr.sh
new file mode 100755
index 00000000..934a75dd
--- /dev/null
+++ b/scripts/mutation-pr.sh
@@ -0,0 +1,185 @@
+#!/usr/bin/env bash
+#
+# Diff-based mutation testing for pull requests.
+#
+# Runs cargo-mutants on Rust files touched by the PR (vs. the base ref),
+# capping wall-clock time at MUTATION_TIMEOUT_SECONDS so PR CI stays under
+# the 30 min budget. Files outside the curated coverage list (router,
+# dispatch, classify, dlp) are skipped — they were not part of the audited
+# mutation scope.
+#
+# Usage: scripts/mutation-pr.sh [BASE_REF]
+#   BASE_REF defaults to origin/main.
+#
+# Environment:
+#   MUTATION_TIMEOUT_SECONDS  Hard wall-clock cap (default: 1500 = 25 min).
+#   MUTATION_PER_MUTANT_TIMEOUT  cargo-mutants per-mutant timeout (default: 120).
+#   GITHUB_OUTPUT             If set, writes status keys for the workflow.
+#
+# Exit codes:
+#   0  Mutation testing converged within the time budget (clean run).
+#   1  cargo-mutants reported surviving mutations or unexpected failure.
+#   2  Time budget exhausted before convergence (PR is informational only).
+#   3  No Rust files in scope — caller should skip the job.
+
+set -euo pipefail
+
+readonly SCRIPT_NAME="$(basename "$0")"
+readonly BASE_REF="${1:-origin/main}"
+readonly TIMEOUT_SECONDS="${MUTATION_TIMEOUT_SECONDS:-1500}"
+readonly PER_MUTANT_TIMEOUT="${MUTATION_PER_MUTANT_TIMEOUT:-120}"
+
+# Curated scope: files where we have invested in mutation coverage. Limiting
+# the PR run to these paths keeps signal high (no false alarms from modules
+# that have never been mutation-tested) and runtime bounded.
+readonly -a SCOPE_PREFIXES=(
+  "src/router/"
+  "src/server/dispatch/"
+  "src/routing/classify/"
+  "src/features/dlp/"
+)
+
+log() { printf '[%s] %s\n' "${SCRIPT_NAME}" "$*" >&2; }
+
+emit() {
+  # Append "key=value" to GITHUB_OUTPUT when running inside Actions.
+  local key="$1" value="$2"
+  if [[ -n "${GITHUB_OUTPUT:-}" ]]; then
+    printf '%s=%s\n' "${key}" "${value}" >>"${GITHUB_OUTPUT}"
+  fi
+}
+
+in_scope() {
+  local file="$1" prefix
+  for prefix in "${SCOPE_PREFIXES[@]}"; do
+    [[ "${file}" == "${prefix}"* ]] && return 0
+  done
+  return 1
+}
+
+main() {
+  log "Base ref: ${BASE_REF}"
+  log "Wall-clock cap: ${TIMEOUT_SECONDS}s, per-mutant cap: ${PER_MUTANT_TIMEOUT}s"
+
+  # Resolve the diff base. In CI we may need to fetch the base ref first.
+  if ! git rev-parse --verify "${BASE_REF}" >/dev/null 2>&1; then
+    log "Cannot resolve ${BASE_REF}; attempting fetch."
+    git fetch --no-tags --depth=50 origin "${BASE_REF#origin/}" || true
+  fi
+
+  # `name-only` + `--diff-filter=ACMR` keeps Added/Copied/Modified/Renamed,
+  # excludes Deleted (cargo-mutants can't mutate a file that was removed).
+  local merge_base
+  merge_base="$(git merge-base "${BASE_REF}" HEAD 2>/dev/null || echo "${BASE_REF}")"
+  log "Merge base: ${merge_base}"
+
+  # Filter by extension in shell rather than via pathspec — avoids relying
+  # on `:(glob)` semantics that vary across git versions on different runners.
+  # Path filter `-- src` keeps git's diff scoped to the source tree; the
+  # `*.rs` suffix and `src/` prefix tests below ensure arbitrary nesting.
+  local -a all_changed=()
+  while IFS= read -r line; do
+    [[ "${line}" == src/* && "${line}" == *.rs ]] || continue
+    all_changed+=("${line}")
+  done < <(git diff --name-only --diff-filter=ACMR "${merge_base}...HEAD" -- src || true)
+
+  if [[ "${#all_changed[@]}" -eq 0 ]]; then
+    log "No Rust source files changed vs. ${BASE_REF}."
+    emit "status" "skipped-no-rust"
+    exit 3
+  fi
+
+  log "Changed Rust files (${#all_changed[@]}):"
+  printf '  - %s\n' "${all_changed[@]}" >&2
+
+  local -a in_scope_files=()
+  local f
+  for f in "${all_changed[@]}"; do
+    if in_scope "${f}"; then
+      in_scope_files+=("${f}")
+    fi
+  done
+
+  if [[ "${#in_scope_files[@]}" -eq 0 ]]; then
+    log "No changed files fall within mutation-tested scope."
+    emit "status" "skipped-out-of-scope"
+    exit 3
+  fi
+
+  log "Files in mutation scope (${#in_scope_files[@]}):"
+  printf '  - %s\n' "${in_scope_files[@]}" >&2
+
+  # Build --file ARG for each in-scope file.
+  local -a mutants_args=()
+  for f in "${in_scope_files[@]}"; do
+    mutants_args+=(--file "${f}")
+  done
+
+  local start_ts end_ts duration_s exit_code=0
+  start_ts="$(date +%s)"
+
+  # `timeout --foreground` so SIGTERM propagates to cargo-mutants and its
+  # cargo subprocesses; `--preserve-status` so we can distinguish a real
+  # cargo-mutants failure from the wall-clock kill.
+  set +e
+  timeout --foreground --preserve-status "${TIMEOUT_SECONDS}" \
+    cargo mutants \
+      --package grob \
+      --timeout "${PER_MUTANT_TIMEOUT}" \
+      -j 2 \
+      --no-shuffle \
+      --colors=never \
+      "${mutants_args[@]}" \
+      -- --lib
+  exit_code=$?
+  set -e
+
+  end_ts="$(date +%s)"
+  duration_s=$((end_ts - start_ts))
+  log "cargo-mutants duration: ${duration_s}s, exit: ${exit_code}"
+
+  # Parse a coarse summary from mutants.out/outcomes.json if produced.
+  # cargo-mutants writes a single JSON document of shape {"outcomes": [...]}.
+  # Each outcome carries a `summary` field with values CAUGHT, MISSED,
+  # TIMEOUT, UNVIABLE, FAILURE, SUCCESS. We project on `summary` rather than
+  # the top-level shape to stay forward-compatible.
+  local total=0 caught=0 missed=0 timeout_n=0 unviable=0
+  if [[ -r mutants.out/outcomes.json ]] && command -v jq >/dev/null 2>&1; then
+    # `..` walks the entire tree to find every `summary` field, regardless
+    # of whether outcomes are at the root or nested under `outcomes:`.
+    total=$(jq '[.. | objects | select(has("summary"))] | length' mutants.out/outcomes.json 2>/dev/null || echo 0)
+    caught=$(jq '[.. | objects | select(.summary == "CAUGHT")] | length' mutants.out/outcomes.json 2>/dev/null || echo 0)
+    missed=$(jq '[.. | objects | select(.summary == "MISSED")] | length' mutants.out/outcomes.json 2>/dev/null || echo 0)
+    timeout_n=$(jq '[.. | objects | select(.summary == "TIMEOUT")] | length' mutants.out/outcomes.json 2>/dev/null || echo 0)
+    unviable=$(jq '[.. | objects | select(.summary == "UNVIABLE")] | length' mutants.out/outcomes.json 2>/dev/null || echo 0)
+  fi
+
+  emit "duration_s" "${duration_s}"
+  emit "exit_code" "${exit_code}"
+  emit "total" "${total}"
+  emit "caught" "${caught}"
+  emit "missed" "${missed}"
+  emit "timeout" "${timeout_n}"
+  emit "unviable" "${unviable}"
+
+  # `timeout` exits 124 on SIGTERM, 137 on SIGKILL when --preserve-status is
+  # absent; with --preserve-status, exit_code reflects cargo-mutants' last
+  # state. We can't distinguish reliably — fall back on duration.
+  if (( duration_s >= TIMEOUT_SECONDS - 5 )); then
+    log "Wall-clock budget exhausted (${duration_s}s >= ${TIMEOUT_SECONDS}s)."
+    emit "status" "timed-out"
+    exit 2
+  fi
+
+  if (( exit_code == 0 )); then
+    log "Mutation testing clean (caught=${caught}, total=${total})."
+    emit "status" "clean"
+    exit 0
+  fi
+
+  log "Mutation testing surfaced ${missed} missed mutant(s)."
+  emit "status" "missed"
+  exit 1
+}
+
+main "$@"

From f514e207f0e15bbcb22d9ded8fe31331d55ccba6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20LIARD?= <ludwig@MacBook-Pro-de-Clement.local>
Date: Tue, 28 Apr 2026 22:44:20 +0200
Subject: [PATCH 2/3] ci(mutants): switch PR comment body to heredoc echos for
 shellcheck SC2016

actionlint's shellcheck integration flagged the prior `printf '%s\n...'`
single-quoted format string with SC2016 (backtick characters in markdown
backticks misread as command substitution candidates). Replace the
printf with `{ echo ... } >file` and feed `gh pr comment --body-file`
plus `gh api --method PATCH` via `jq -Rs '{body: .}'`. Same external
behaviour, no more SC2016 noise.
---
 .github/workflows/ci.yml | 47 ++++++++++++++++++++++++++++++----------
 1 file changed, 36 insertions(+), 11 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8f51e1df..1e7aef86 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -620,24 +620,49 @@ jobs:
           UNVIABLE: ${{ steps.mutate.outputs.unviable || 'n/a' }}
           ARTIFACT: mutants-pr-results-${{ github.sha }}
         run: |
-          # Render a compact comment body, then upsert via gh api so re-runs
-          # update a single comment instead of spamming the timeline. The
-          # marker line is greppable from past comments.
+          # Build the comment body via heredoc-style echos (no single-quoted
+          # printf format; shellcheck SC2016-friendly). The marker line is
+          # the discriminator we grep for to upsert prior comments.
           MARKER="<!-- mutants-pr-summary -->"
-          BODY="$(printf '%s\n## Mutation testing (PR diff sample)\n\nInformational — never blocks merge. Full matrix on `main`.\n\n| Metric | Value |\n|--------|-------|\n| Status | `%s` |\n| Duration | %s s |\n| Total | %s |\n| Caught | %s |\n| Missed | %s |\n| Timeout | %s |\n| Unviable | %s |\n\nLegend: `clean` (no survivors), `missed` (inspect artifact), `timed-out` (25 min cap reached).\n\nArtifact: `%s`.\n' \
-            "${MARKER}" "${STATUS}" "${DURATION}" "${TOTAL}" "${CAUGHT}" "${MISSED}" "${TIMEOUT_N}" "${UNVIABLE}" "${ARTIFACT}")"
+          BODY_FILE="$(mktemp)"
+          {
+            echo "${MARKER}"
+            echo "## Mutation testing (PR diff sample)"
+            echo
+            echo "Informational — never blocks merge. Full matrix runs on main."
+            echo
+            echo "| Metric | Value |"
+            echo "|--------|-------|"
+            echo "| Status | ${STATUS} |"
+            echo "| Duration | ${DURATION} s |"
+            echo "| Total | ${TOTAL} |"
+            echo "| Caught | ${CAUGHT} |"
+            echo "| Missed | ${MISSED} |"
+            echo "| Timeout | ${TIMEOUT_N} |"
+            echo "| Unviable | ${UNVIABLE} |"
+            echo
+            echo "Legend: clean (no survivors), missed (inspect artifact), timed-out (25 min cap reached)."
+            echo
+            echo "Artifact: ${ARTIFACT}."
+          } >"${BODY_FILE}"
 
-          # Look for an existing summary comment to update; otherwise post a new one.
-          EXISTING_ID="$(gh api "repos/${GITHUB_REPOSITORY}/issues/${PR_NUMBER}/comments" \
-            --jq "[.[] | select(.body | startswith(\"${MARKER}\"))][0].id" || echo "")"
+          # Look for an existing summary comment to update; otherwise post a
+          # new one. `gh issue comment` does not support upsert natively, so
+          # we list comments, filter by marker, and PATCH if found.
+          COMMENTS_URL="repos/${GITHUB_REPOSITORY}/issues/${PR_NUMBER}/comments"
+          EXISTING_ID=$(gh api "${COMMENTS_URL}" --jq "[.[] | select(.body | startswith(\"${MARKER}\"))][0].id" || true)
 
           if [ -n "${EXISTING_ID}" ] && [ "${EXISTING_ID}" != "null" ]; then
-            gh api --method PATCH "repos/${GITHUB_REPOSITORY}/issues/comments/${EXISTING_ID}" \
-              -f body="${BODY}" >/dev/null
+            # PATCH a comment by ID — body comes from the file via jq -Rs,
+            # which slurps the whole file as a single JSON string for the
+            # request body envelope.
+            jq -Rs '{body: .}' "${BODY_FILE}" \
+              | gh api --method PATCH "repos/${GITHUB_REPOSITORY}/issues/comments/${EXISTING_ID}" --input - >/dev/null
             echo "Updated existing comment ${EXISTING_ID}."
           else
-            gh pr comment "${PR_NUMBER}" --body "${BODY}"
+            gh pr comment "${PR_NUMBER}" --body-file "${BODY_FILE}"
           fi
+          rm -f "${BODY_FILE}"
 
   # =========================================================================
   # Stage 3: Cross build (main push + tag push only, not PRs)

From fda9f53adaf909195142fe1ec7b37eb8db988834 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20LIARD?= <ludwig@MacBook-Pro-de-Clement.local>
Date: Tue, 28 Apr 2026 22:48:26 +0200
Subject: [PATCH 3/3] ci(mutants): strip backticks from job-summary echos to
 settle SC2016
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Backticks in echos that wrap shell variables can be parsed by shellcheck
as command substitution candidates — even when escaped — and the
actionlint+shellcheck combo running in CI flagged them. Replace with
plain ASCII delimiters in the job-summary output and the comment-body
echos.
---
 .github/workflows/ci.yml | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1e7aef86..0eb8f854 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -585,14 +585,16 @@ jobs:
           UNVIABLE: ${{ steps.mutate.outputs.unviable || 'n/a' }}
           ARTIFACT: mutants-pr-results-${{ github.sha }}
         run: |
+          # Plain ASCII output — backticks elided to dodge shellcheck SC2016
+          # noise inside the actionlint pipeline.
           {
             echo "## Mutation testing (PR diff sample)"
             echo
-            echo "Informational only — never blocks merge. Full matrix runs on \`main\`."
+            echo "Informational only — never blocks merge. Full matrix runs on main."
             echo
             echo "| Metric | Value |"
             echo "|--------|-------|"
-            echo "| Status | \`${STATUS}\` |"
+            echo "| Status | ${STATUS} |"
             echo "| Duration | ${DURATION} s |"
             echo "| Total mutants | ${TOTAL} |"
             echo "| Caught | ${CAUGHT} |"
@@ -600,10 +602,10 @@ jobs:
             echo "| Timeout | ${TIMEOUT_N} |"
             echo "| Unviable | ${UNVIABLE} |"
             echo
-            echo "Status legend: \`clean\` (no survivors), \`missed\` (inspect artifact),"
-            echo "\`timed-out\` (25 min cap reached), \`skipped-*\` (no in-scope diff)."
+            echo "Status legend: clean (no survivors), missed (inspect artifact),"
+            echo "timed-out (25 min cap reached), skipped-* (no in-scope diff)."
             echo
-            echo "Artifact: \`${ARTIFACT}\`."
+            echo "Artifact: ${ARTIFACT}."
           } >>"${GITHUB_STEP_SUMMARY}"
       - name: Comment PR with sampling summary
         # Skip on forks (no token write access) and when nothing was sampled.