Merge pull request #10955 from lightningnetwork/ci/workflow-job-split

ci: split the Claude PR-severity and issue-dedupe workflows into two jobs

.github/workflows/claude-dedupe-issues.yml

@@ -10,26 +10,167 @@ on:
         required: true
         type: string
 
+# Default to read-only. The find-duplicates job reads untrusted issue text with
+# the model, so it must not hold a write token; post-comment takes issues: write
+# but runs no model and only shells out to scripts/comment-on-duplicates.sh,
+# which re-validates every issue number it is handed.
+permissions:
+  contents: read
+
+# Serialize runs for the same issue so an `issues: opened` event and a
+# workflow_dispatch for the same number can't both read "no prior comment" and
+# double-post. Mirrors pr-severity.yml.
+concurrency:
+  group: claude-dedupe-${{ github.event.issue.number || inputs.issue_number }}
+  cancel-in-progress: true
+
 jobs:
-  claude-dedupe-issues:
+  find-duplicates:
     runs-on: ubuntu-latest
     timeout-minutes: 10
+    # Read-only: the model inspects the issue and searches for duplicates, then
+    # records the candidate issue numbers to a file.
     permissions:
       contents: read
-      issues: write
-      id-token: write
+      issues: read
 
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
+        with:
+          persist-credentials: false
 
-      - name: Run Claude Code slash command
-        uses: anthropics/claude-code-action@v1
+      - name: Find duplicate issues with Claude
+        # Pinned to a full commit SHA rather than the mutable @v1 tag: this step
+        # feeds untrusted issue text to the model with CLAUDE_CODE_OAUTH_TOKEN in
+        # process, so a repointed tag would run attacker-controlled action code
+        # with that secret present. Bump deliberately when updating.
+        uses: anthropics/claude-code-action@ba0aafd4308cbba7165f9f2cdb0cfbed5a3c99ce # v1
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
+          claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
+
+          # Accept any issue author: this job holds only read scope and merely
+          # records candidate issue numbers to a file; the comment is posted by
+          # a separate, model-free job. "*" is safe ONLY while this job stays
+          # read-only. Before granting this job a write token or a mutating tool
+          # (a write-capable gh subcommand, a Bash mutation), replace "*" with
+          # an explicit allowlist — otherwise any fork author's issue text would
+          # steer a privileged model.
           allowed_non_write_users: "*"
           model: claude-haiku-4-5-20251001
-          prompt: "/dedupe ${{ github.repository }}/issues/${{ github.event.issue.number || inputs.issue_number }}"
-          claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
+
+          # Read-only gh tools plus Write to record the result. No comment or
+          # edit tools, and no access to the duplicate-comment script.
+          claude_args: >-
+            --allowedTools
+            "Bash(gh issue view:*)"
+            "Bash(gh search:*)"
+            "Bash(gh issue list:*)"
+            "Write"
+
+          prompt: |
+            Find up to 3 likely duplicate issues for issue
+            #${{ github.event.issue.number || inputs.issue_number }} in the
+            ${{ github.repository }} repository. Follow these steps precisely:
+
+            1. View the issue and check whether it (a) is closed, (b) does not
+               need deduping (e.g. broad product feedback without a specific
+               solution, or positive feedback), or (c) already has a duplicates
+               comment. If any of these hold, write an empty `duplicates.txt`
+               (create the file with no content) and stop.
+
+            2. Summarize the issue.
+
+            3. Search GitHub for duplicates of this issue using several diverse
+               keyword searches and search approaches, based on the summary.
+
+            4. Filter out false positives that are likely not actually
+               duplicates of the original issue. If no plausible duplicates
+               remain, write an empty `duplicates.txt` and stop.
+
+            5. Otherwise, write the chosen duplicate issue numbers to a file
+               named `duplicates.txt` in the current working directory: digits
+               only, one issue number per line, at most 3 lines. Do not include
+               `#`, URLs, or any other text.
+
+            Notes:
+            - Use `gh` to interact with GitHub, not web fetch.
+            - Do NOT use any tools beyond `gh issue view`, `gh search`,
+              `gh issue list`, and `Write`. You do NOT post comments; a separate
+              step does that from the file you write.
+            - Make a todo list first.
+
+      - name: Upload duplicate candidates
+        uses: actions/upload-artifact@v4
+        with:
+          name: dedupe-result
+          path: duplicates.txt
+          if-no-files-found: warn
+          retention-days: 1
+
+  post-comment:
+    runs-on: ubuntu-latest
+    needs: find-duplicates
+    timeout-minutes: 5
+    # Write scope lives here, in a job that runs no model. The base issue number
+    # comes from the trusted event payload, and comment-on-duplicates.sh
+    # re-validates every candidate issue number before posting.
+    permissions:
+      contents: read
+      issues: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+
+      - name: Download duplicate candidates
+        uses: actions/download-artifact@v4
+        # find-duplicates uploads with if-no-files-found: warn, so when the
+        # model writes no file at all (timeout, refusal) no artifact exists and
+        # download-artifact would otherwise hard-fail the job. Tolerate a
+        # missing artifact so the no-op guard in the next step is reachable.
+        continue-on-error: true
+        with:
+          name: dedupe-result
+          path: result
+
+      - name: Post duplicate comment
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_REPOSITORY: ${{ github.repository }}
+          BASE_ISSUE: ${{ github.event.issue.number || inputs.issue_number }}
+        run: |
+          set -euo pipefail
+
+          # Distinguish a genuine "no duplicates" verdict from a find-duplicates
+          # run that produced no artifact at all (model crash/timeout, or a
+          # tolerated missing-artifact download). The latter gets a warning so a
+          # broken run doesn't read as a healthy no-op, mirroring the pr-severity
+          # apply step; the present-but-empty case stays a silent no-op.
+          if [[ ! -f result/duplicates.txt ]]; then
+            echo "::warning::dedupe find-duplicates produced no result; nothing posted."
+            exit 0
+          fi
+          if [[ ! -s result/duplicates.txt ]]; then
+            echo "No duplicate candidates; nothing to post."
+            exit 0
+          fi
+
+          # Extract up to 3 purely-numeric issue ids. comment-on-duplicates.sh
+          # re-validates these and the base issue (numeric, existing, at most 3)
+          # before posting.
+          mapfile -t DUPS < <(grep -oE '^[0-9]+$' result/duplicates.txt | head -n 3)
+
+          if [[ ${#DUPS[@]} -eq 0 ]]; then
+            echo "No valid numeric duplicate ids; nothing to post."
+            exit 0
+          fi
+
+          ./scripts/comment-on-duplicates.sh \
+            --base-issue "$BASE_ISSUE" \
+            --potential-duplicates "${DUPS[@]}"

.github/workflows/pr-severity.yml

@@ -1,16 +1,19 @@
 name: PR Severity Classification
 
 on:
-  # Use pull_request_target to allow running on fork PRs with access to secrets.
-  # This is safe because we don't checkout or execute any code from the PR -
-  # we only read PR metadata (changed files, labels) via the GitHub API.
+  # Use pull_request_target so the workflow runs on fork PRs with the base
+  # repository's workflow definition. The classify job below reads PR metadata
+  # with a read-only token and never checks out or executes PR code; the write
+  # scope needed to apply the label lives in a separate, model-free job.
   pull_request_target:
     types: [opened, synchronize, labeled]
 
+# Default the whole workflow to read-only. Each job opts into exactly the scope
+# it needs: classify stays read-only (untrusted PR metadata reaches the model,
+# so it must not hold a write token), apply takes pull-requests: write but runs
+# no model.
 permissions:
   contents: read
-  pull-requests: write
-  issues: write
 
 concurrency:
   group: pr-severity-${{ github.event.pull_request.number }}
@@ -20,6 +23,14 @@ jobs:
   classify:
     name: Classify PR Severity
     runs-on: ubuntu-latest
+    # Cap the model run: it fires on every pull_request_target synchronize with
+    # attacker-controllable input, so bound its runner-minute/token cost rather
+    # than inheriting GitHub's 6h default. Mirrors the dedupe workflow.
+    timeout-minutes: 10
+    # Read-only: the classifier only inspects PR metadata via the GitHub API.
+    permissions:
+      contents: read
+      pull-requests: read
     # Skip if PR has skip-severity-check label.
     # For labeled events, only run if 'reclassify' label was added.
     if: |
@@ -30,43 +41,78 @@ jobs:
         uses: actions/checkout@v4
         with:
           fetch-depth: 1
+          # Don't leave the job token in .git/config: nothing here needs a
+          # persisted git credential, and the classifier runs on untrusted
+          # fork-PR input.
+          persist-credentials: false
 
       - name: Classify PR with Claude
-        uses: anthropics/claude-code-action@v1
+        # Pinned to a full commit SHA rather than the mutable @v1 tag: this step
+        # runs on pull_request_target with CLAUDE_CODE_OAUTH_TOKEN and
+        # GITHUB_TOKEN in-process and is reachable by any fork author, so a
+        # repointed tag would run attacker-controlled action code with those
+        # secrets present. Bump deliberately when updating.
+        uses: anthropics/claude-code-action@ba0aafd4308cbba7165f9f2cdb0cfbed5a3c99ce # v1
+        env:
+          # gh (invoked by the Bash(gh pr view) tool) authenticates from
+          # GH_TOKEN; set it explicitly so classification doesn't depend on the
+          # action propagating its github_token input into the tool environment,
+          # matching the dedupe find-duplicates step.
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
           claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
           github_token: ${{ secrets.GITHUB_TOKEN }}
 
-          # Allow any user since this workflow only reads PR metadata via API
-          # and doesn't execute any code from the PR. Tool permissions are
-          # restricted to gh pr commands only.
+          # Accept any PR author: this job holds only a read-only token, reads
+          # PR metadata via the API, and writes its verdict to a file. The
+          # privileged label/comment step runs separately without the model.
+          # "*" is safe ONLY while this job stays read-only. Before granting it
+          # a write token or a mutating tool (a write-capable gh subcommand, a
+          # Bash mutation), replace "*" with an explicit allowlist — otherwise
+          # any fork author's PR text would steer a privileged model.
           allowed_non_write_users: "*"
 
-          # Allow Claude to manage labels and post comments.
-          # Keep permissions minimal to limit prompt injection risk.
-          claude_args: --allowedTools "Bash(gh pr view:*)" "Bash(gh pr edit:*)" "Bash(gh pr comment:*)"
+          # Pin the model so the severity decision (which gates the label the
+          # apply job applies) is reproducible from the workflow file and does
+          # not drift on an action-default change.
+          model: claude-sonnet-5
+
+          # The classifier only needs to read PR data and record its verdict to
+          # the workspace. It has no write-capable gh tools.
+          #
+          # Security note: because this runs on pull_request_target, the OAuth
+          # token above is present in-process while the model reads untrusted
+          # fork-PR text. The read-only github_token bounds what the model can
+          # WRITE via the API, but the in-process token's protection rests on
+          # this allowlist staying minimal — read-only `gh pr view` plus
+          # `Write`, with no network- or shell-mutating tool a prompt injection
+          # could use to exfiltrate it. Keep it that way: do not add `Bash`
+          # verbs beyond `gh pr view`, and never add a tool that can make
+          # outbound requests. (A stricter design would drop Bash entirely and
+          # pre-fetch PR metadata via the API in a separate step.)
+          claude_args: --allowedTools "Bash(gh pr view:*)" "Write"
 
           prompt: |
             You are a PR severity classifier for the lnd (Lightning Network Daemon) repository.
 
             ## Tool Constraints
 
-            You ONLY have access to these commands:
+            You ONLY have access to:
             - `gh pr view` - to read PR metadata
-            - `gh pr edit` - to add/remove labels
-            - `gh pr comment` - to post comments
+            - `Write` - to record your verdict to files
 
-            You do NOT have access to `gh api`, `gh label`, or any other
-            `gh` subcommand. Do not attempt to use them. For ALL label
-            operations, use `gh pr edit` with `--add-label` or
-            `--remove-label`.
+            You do NOT have access to `gh api`, `gh label`, `gh pr edit`,
+            `gh pr comment`, or any other command. Do not attempt to use them.
+            You do NOT apply labels or post comments yourself. A separate,
+            deterministic step reads the files you write and applies the label
+            and comment. Your job is only to classify and record the result.
 
             ## Your Task
 
             Analyze PR #${{ github.event.pull_request.number }} and:
             1. Determine its severity level based on the files changed
-            2. Apply the appropriate severity label
-            3. Post a detailed comment explaining your determination
+            2. Record the severity, whether a comment should be posted, and the
+               comment body, to files (see "Output" below).
 
             ## Severity Levels
 
@@ -130,51 +176,49 @@ jobs:
 
             ## Steps
 
-            1. First, check for existing override labels AND existing severity labels:
+            1. Read the current labels AND comments to detect overrides and prior
+               bot activity:
                ```
-               gh pr view ${{ github.event.pull_request.number }} --json labels --jq '.labels[].name'
+               gh pr view ${{ github.event.pull_request.number }} --json labels,comments
                ```
-               Note which `severity-*` label (if any) is currently applied. This is
-               the "previous severity".
+               Note which `severity-*` label (if any) is currently applied. This
+               is the "previous severity". Look for the HTML marker
+               `<!-- pr-severity-bot -->` in comment bodies to tell whether the
+               bot has commented before.
 
-            2. If an override label exists (severity-override-*), use that level and skip classification.
+            2. If an override label exists (severity-override-*), use that level
+               and skip classification.
 
-            3. Check for existing bot comments. Look for the HTML marker `<!-- pr-severity-bot -->`:
-               ```
-               gh pr view ${{ github.event.pull_request.number }} --json comments --jq '.comments[].body' | grep -c 'pr-severity-bot' || true
-               ```
-               This tells you whether the bot has commented before.
-
-            4. Get the list of changed files:
+            3. Get the list of changed files:
                ```
                gh pr view ${{ github.event.pull_request.number }} --json files,additions,deletions
                ```
 
-            5. Classify each file and determine the new overall severity.
+            4. Classify each file and determine the new overall severity.
 
-            6. **Decide whether to comment.** Only post a comment if EITHER:
-               - The bot has NOT commented before (no existing comment with `<!-- pr-severity-bot -->`), OR
-               - The newly determined severity is DIFFERENT from the previous severity label.
+            5. **Decide whether a comment should be posted.** Set should_comment
+               to "true" only if EITHER:
+               - The bot has NOT commented before (no existing comment with
+                 `<!-- pr-severity-bot -->`), OR
+               - The newly determined severity is DIFFERENT from the previous
+                 severity label.
 
-               If the bot already commented AND the severity has NOT changed, just
-               stop here — do NOT post another comment. Still update the label if
-               needed (step 7-8), but skip the comment.
+               Otherwise set should_comment to "false" (the label may still be
+               updated by the apply step, but no new comment is posted).
 
-            7. Remove any existing severity-* labels (not override labels):
-               ```
-               gh pr edit ${{ github.event.pull_request.number }} --remove-label "severity-critical" 2>/dev/null || true
-               gh pr edit ${{ github.event.pull_request.number }} --remove-label "severity-high" 2>/dev/null || true
-               gh pr edit ${{ github.event.pull_request.number }} --remove-label "severity-medium" 2>/dev/null || true
-               gh pr edit ${{ github.event.pull_request.number }} --remove-label "severity-low" 2>/dev/null || true
-               ```
+            ## Output
 
-            8. Apply the new severity label:
-               ```
-               gh pr edit ${{ github.event.pull_request.number }} --add-label "severity-<level>"
-               ```
+            Record your verdict by writing these files in the current working
+            directory (the repository root). Do NOT apply labels or comment
+            yourself.
 
-            9. If you determined in step 6 that a comment should be posted, post it
-               with your analysis. Use this format:
+            1. `severity.txt` - exactly one lowercase word, one of:
+               `critical`, `high`, `medium`, `low`. Nothing else.
+
+            2. `should_comment.txt` - exactly `true` or `false`.
+
+            3. `comment.md` - only if should_comment is `true`. The full comment
+               markdown, in this format:
 
                If this is a severity CHANGE (previous label existed but differs),
                prepend: `> ⚠️ Severity changed: **<OLD>** → **<NEW>** (files changed since last classification)`
@@ -203,16 +247,67 @@ jobs:
                <!-- pr-severity-bot -->
                ```
 
-            10. Post the comment using `gh pr comment`:
-               ```
-               gh pr comment ${{ github.event.pull_request.number }} --body "YOUR_COMMENT_HERE"
-               ```
+               If should_comment is `false`, do not create `comment.md`.
 
-            11. If you decided in step 6 to SKIP commenting, do NOT post any comment.
-                Just ensure the label is correct and exit.
+               Keep the comment concise and factual: it is posted verbatim under
+               the bot's identity, and the apply step defangs any `@`-mentions
+               and links, so do not rely on them.
 
             ## Emoji Mapping
             - critical: 🔴
             - high: 🟠
             - medium: 🟡
             - low: 🟢
+
+      - name: Upload classification result
+        uses: actions/upload-artifact@v4
+        with:
+          name: pr-severity-result
+          path: |
+            severity.txt
+            should_comment.txt
+            comment.md
+          if-no-files-found: warn
+          retention-days: 1
+
+  apply:
+    name: Apply Severity Label
+    runs-on: ubuntu-latest
+    needs: classify
+    timeout-minutes: 5
+    # Write scope lives here, in a job that runs no model. The only inputs are
+    # the PR number from the trusted event payload and the classifier's files,
+    # which are strictly validated before use.
+    permissions:
+      contents: read
+      pull-requests: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          # Needed for scripts/apply-pr-severity.sh; no persisted git credential
+          # is required here.
+          persist-credentials: false
+
+      - name: Download classification result
+        uses: actions/download-artifact@v4
+        # classify uploads with if-no-files-found: warn, so if the model writes
+        # no verdict at all (timeout, refusal) no artifact exists and
+        # download-artifact would otherwise hard-fail the job. Tolerate a
+        # missing artifact so the no-op guard in the next step is reachable.
+        continue-on-error: true
+        with:
+          name: pr-severity-result
+          path: result
+
+      - name: Apply label and comment
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          REPO: ${{ github.repository }}
+        # Validate the severity, reconcile the label, and sanitize + post the
+        # model-authored comment. The logic lives in a checked-in script so the
+        # untrusted-comment sanitizer is unit-tested
+        # (scripts/apply-pr-severity_test.sh), mirroring how the dedupe workflow
+        # delegates to scripts/comment-on-duplicates.sh.
+        run: ./scripts/apply-pr-severity.sh result

scripts/apply-pr-severity.sh

@@ -0,0 +1,145 @@
+#!/usr/bin/env bash
+#
+# Applies the PR severity label and posts the classifier's comment.
+#
+# Reads the classifier's verdict from a result directory (arg $1, default
+# "result") and, in this order:
+#   - validates the severity against the known set,
+#   - reconciles the severity-* label in a single gh edit, and
+#   - sanitizes and posts the model-authored comment.
+#
+# The classify job runs a model on untrusted PR text, so the comment body is
+# treated as tainted and passed through sanitize_comment() before posting.
+#
+# Env: GH_TOKEN (gh auth), PR_NUMBER, REPO.
+# Usage: ./apply-pr-severity.sh [RESULT_DIR]
+
+set -euo pipefail
+
+# sanitize_comment reads an untrusted comment body on stdin and writes a safe
+# version to stdout. GitHub already strips scripts and unsafe HTML from rendered
+# comment bodies, so this targets the notification/spam class: @-mentions that
+# ping arbitrary users, `#N` cross-references that notify other issues/PRs,
+# auto-linked URLs used for phishing, and Markdown links. It deliberately leaves
+# the model's <details>/<sub> markup intact so the comment still renders.
+#
+# The zero-width non-joiner is spliced in as a literal byte (not a `\xNN` sed
+# escape) so the rules work identically under both GNU and BSD sed. Rule order
+# matters: the `#`-before-digit defang runs before the bracket rules, which
+# themselves emit `&#91;`/`&#93;` — running it after would corrupt those
+# entities. Matching only `#` followed by a digit leaves `##`/`###` Markdown
+# headings untouched.
+sanitize_comment() {
+  local z
+  z="$(printf '\xe2\x80\x8c')"
+  sed -E \
+    -e "s/@/@${z}/g" \
+    -e "s/www\./www${z}./g" \
+    -e 's,[hH][tT][tT][pP][sS]?://,hxxp://,g' \
+    -e "s/#([0-9])/#${z}\1/g" \
+    -e 's/\[/\&#91;/g' \
+    -e 's/\]/\&#93;/g'
+}
+
+main() {
+  local result_dir="${1:-result}"
+  : "${GH_TOKEN:?GH_TOKEN is required}"
+  : "${PR_NUMBER:?PR_NUMBER is required}"
+  : "${REPO:?REPO is required}"
+
+  # Treat a missing severity.txt and an empty/whitespace-only one the same way:
+  # both mean the classify job produced no usable verdict (model crash or
+  # timeout, a missing artifact tolerated by the download step, or a truncated
+  # write). Warn and degrade rather than laundering a broken run into a silent
+  # green or failing the check red, since severity classification is advisory.
+  # A non-empty but unrecognized value still fails below.
+  #
+  # Lowercase on read so a stray `Low`/`HIGH` from the model still matches.
+  local severity=""
+  if [[ -f "$result_dir/severity.txt" ]]; then
+    severity="$(tr -d '[:space:]' < "$result_dir/severity.txt" | tr '[:upper:]' '[:lower:]')"
+  fi
+  if [[ -z "$severity" ]]; then
+    echo "::warning::PR severity classifier produced no verdict; PR left unlabeled."
+    return 0
+  fi
+
+  # Strictly validate the severity against the known set — it is the only
+  # privileged, semantically meaningful output.
+  case "$severity" in
+    critical|high|medium|low) ;;
+    *)
+      echo "Invalid severity '$severity'; refusing to apply." >&2
+      return 1
+      ;;
+  esac
+
+  # Read the PR's current severity-* labels so the reconciliation below removes
+  # exactly the ones present. (The severity-change banner is authored by the
+  # model in comment.md, so no previous severity is needed here.)
+  #
+  # Fail closed on a read error (rate limit, 5xx): swallowing it would yield
+  # empty labels, so the loop below would remove nothing yet still add the new
+  # label — the exact two-label state this single-edit design prevents. With
+  # set -e, a failed read aborts before any edit. (local is declared separately
+  # so the assignment's own exit status, not local's, drives set -e.)
+  local cur_labels
+  cur_labels="$(gh pr view "$PR_NUMBER" --repo "$REPO" \
+    --json labels --jq '.labels[].name')"
+
+  # Reconcile the severity label in a SINGLE gh edit: add the target and remove
+  # exactly the other severity-* labels currently present. Doing it in one call
+  # means:
+  #   - if the add fails (label missing from the repo, transient API error), the
+  #     whole edit fails and the PR keeps its prior label rather than being left
+  #     unlabeled; and
+  #   - a run cancelled by `concurrency.cancel-in-progress` can't stop between an
+  #     add and a separate remove, so the PR is never left carrying two labels.
+  # Only present labels are removed, so gh never errors on a missing one.
+  local edit_args level
+  edit_args=(--add-label "severity-$severity")
+  for level in critical high medium low; do
+    [[ "$level" == "$severity" ]] && continue
+    if grep -qx "severity-$level" <<< "$cur_labels"; then
+      edit_args+=(--remove-label "severity-$level")
+    fi
+  done
+  gh pr edit "$PR_NUMBER" --repo "$REPO" "${edit_args[@]}"
+
+  # Lowercase on read (as with severity) so a `True`/`TRUE` slip from the model
+  # is honored rather than silently dropping the comment.
+  local should_comment="false"
+  if [[ -f "$result_dir/should_comment.txt" ]]; then
+    should_comment="$(tr -d '[:space:]' < "$result_dir/should_comment.txt" | tr '[:upper:]' '[:lower:]')"
+  fi
+
+  # Use -s (exists and non-empty): a 0-byte comment.md would otherwise reach
+  # `gh pr comment --body-file`, which rejects an empty body and would abort
+  # after the label was already applied.
+  if [[ "$should_comment" != "true" || ! -s "$result_dir/comment.md" ]]; then
+    echo "No comment requested; done."
+    return 0
+  fi
+
+  # Sanitize first, then enforce the size cap on the SANITIZED body. Every
+  # sanitizer rule only grows the byte count (e.g. `[` -> `&#91;`), so a body
+  # that fits before sanitizing can exceed GitHub's comment limit afterward;
+  # measuring the post-sanitization size is what actually bounds the request.
+  sanitize_comment < "$result_dir/comment.md" > "$result_dir/comment.sanitized.md"
+
+  local max_bytes=16384
+  if [[ "$(wc -c < "$result_dir/comment.sanitized.md")" -gt "$max_bytes" ]]; then
+    echo "::warning::classifier comment exceeds ${max_bytes} bytes after sanitization; skipping comment."
+    return 0
+  fi
+
+  # Post from a file (never interpolated into the shell) so the body is handled
+  # purely as data.
+  gh pr comment "$PR_NUMBER" --repo "$REPO" \
+    --body-file "$result_dir/comment.sanitized.md"
+}
+
+# Allow sourcing (e.g. from the test) without executing main.
+if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
+  main "$@"
+fi

scripts/apply-pr-severity_test.sh

@@ -0,0 +1,125 @@
+#!/usr/bin/env bash
+#
+# Tests for scripts/apply-pr-severity.sh: the sanitize_comment() filter and the
+# main() control flow (label reconciliation and comment gating), the latter with
+# gh stubbed via a PATH shim that records its argument lists.
+#
+# Run: bash scripts/apply-pr-severity_test.sh
+
+set -euo pipefail
+
+DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+# shellcheck source=scripts/apply-pr-severity.sh
+source "$DIR/apply-pr-severity.sh"
+
+ZWNJ="$(printf '\xe2\x80\x8c')"
+fail=0
+
+want()   { grep -qF -- "$2" <<< "$OUT"   && echo "ok:   $1" || { echo "FAIL: $1"; fail=1; }; }
+absent() { grep -qF -- "$2" <<< "$OUT"   && { echo "FAIL: $1"; fail=1; } || echo "ok:   $1"; }
+eq()     { [[ "$2" == "$3" ]]            && echo "ok:   $1" || { echo "FAIL: $1 (got '$2' want '$3')"; fail=1; }; }
+has()    { grep -qF -- "$2" "$GH_CALLS"  && echo "ok:   $1" || { echo "FAIL: $1 (no gh call: $2)"; fail=1; }; }
+lacks()  { grep -qF -- "$2" "$GH_CALLS"  && { echo "FAIL: $1 (unexpected gh call: $2)"; fail=1; } || echo "ok:   $1"; }
+in_file(){ grep -qF -- "$3" "$2"         && echo "ok:   $1" || { echo "FAIL: $1"; fail=1; }; }
+
+echo "# sanitize_comment"
+INPUT='## 🟢 PR Severity: **LOW**
+### Analysis
+Ping @user, see #123 and org/repo#4567, [x](https://evil), www.evil.net, http://Bad.io.
+<!-- pr-severity-bot -->'
+OUT="$(printf '%s' "$INPUT" | sanitize_comment)"
+want   "## heading preserved"              '## 🟢 PR Severity'
+want   "### heading preserved"             '### Analysis'
+want   "@-mention defanged"                "@${ZWNJ}user"
+want   "#123 defanged"                     "#${ZWNJ}123"
+want   "repo#4567 defanged"                "#${ZWNJ}4567"
+want   "https scheme defanged"             'hxxp://evil'
+want   "http scheme (case-insensitive)"    'hxxp://Bad.io'
+want   "www. auto-link defanged"           "www${ZWNJ}.evil.net"
+want   "markdown brackets escaped"         '&#91;x&#93;'
+want   "bot marker preserved"              '<!-- pr-severity-bot -->'
+absent "no live http(s):// scheme"         'https://'
+absent "bracket entity not corrupted by #" "&#${ZWNJ}"
+
+echo "# main()"
+WORK="$(mktemp -d)"
+trap 'rm -rf "$WORK"' EXIT
+mkdir -p "$WORK/bin"
+# Fake gh: record the full argument list, and for `pr view` emit the fixture
+# labels so main()'s reconciliation has something to diff against.
+cat > "$WORK/bin/gh" <<'SH'
+#!/usr/bin/env bash
+echo "$*" >> "$GH_CALLS"
+[[ "$1 $2" == "pr view" ]] && printf '%s' "${GH_FAKE_LABELS:-}"
+exit 0
+SH
+chmod +x "$WORK/bin/gh"
+export PATH="$WORK/bin:$PATH"
+export GH_TOKEN=x PR_NUMBER=42 REPO=owner/repo
+
+# run_main RESULT_DIR: run main() capturing its return code in RC, with a fresh
+# GH_CALLS log for the case.
+run_main() { export GH_CALLS="$WORK/calls"; : > "$GH_CALLS"; RC=0; main "$1" >/dev/null 2>&1 || RC=$?; }
+
+# Invalid severity: reject before any gh mutation.
+r="$WORK/invalid"; mkdir -p "$r"; printf 'bogus\n' > "$r/severity.txt"
+GH_FAKE_LABELS='' run_main "$r"
+eq    "invalid severity returns 1"        "$RC" "1"
+lacks "invalid severity: no label edit"   "pr edit"
+
+# No verdict at all: warn and no-op, no gh mutation.
+r="$WORK/noverdict"; mkdir -p "$r"
+GH_FAKE_LABELS='' run_main "$r"
+eq    "missing severity.txt returns 0"    "$RC" "0"
+lacks "missing verdict: no label edit"    "pr edit"
+
+# Empty/whitespace-only severity.txt is handled like a missing one (F30).
+r="$WORK/emptysev"; mkdir -p "$r"; printf '   \n' > "$r/severity.txt"
+GH_FAKE_LABELS='' run_main "$r"
+eq    "empty severity.txt returns 0"      "$RC" "0"
+lacks "empty severity: no label edit"     "pr edit"
+
+# Valid severity, no comment: reconcile labels in one edit, remove only present.
+r="$WORK/label"; mkdir -p "$r"; printf 'high\n' > "$r/severity.txt"; printf 'false\n' > "$r/should_comment.txt"
+GH_FAKE_LABELS=$'severity-low\nkeep-me\nseverity-medium' run_main "$r"
+eq    "label-only returns 0"              "$RC" "0"
+has   "adds target label"                 "--add-label severity-high"
+has   "removes present severity-low"      "--remove-label severity-low"
+has   "removes present severity-medium"   "--remove-label severity-medium"
+lacks "does not touch absent critical"    "severity-critical"
+lacks "no comment when should_comment false" "pr comment"
+
+# should_comment true with a real body: sanitize and post it.
+r="$WORK/comment"; mkdir -p "$r"; printf 'low\n' > "$r/severity.txt"; printf 'true\n' > "$r/should_comment.txt"
+printf '## x\nhi @bob\n' > "$r/comment.md"
+GH_FAKE_LABELS='' run_main "$r"
+eq      "comment path returns 0"          "$RC" "0"
+has     "posts sanitized comment"         "pr comment 42 --repo owner/repo --body-file"
+in_file "posted body defangs @-mention"   "$r/comment.sanitized.md" "@${ZWNJ}bob"
+
+# Capitalized should_comment is honored, not silently dropped (F31).
+r="$WORK/truecase"; mkdir -p "$r"; printf 'low\n' > "$r/severity.txt"; printf 'TRUE\n' > "$r/should_comment.txt"
+printf '## x\nhi\n' > "$r/comment.md"
+GH_FAKE_LABELS='' run_main "$r"
+eq    "should_comment TRUE returns 0"     "$RC" "0"
+has   "TRUE still posts the comment"      "pr comment 42 --repo owner/repo --body-file"
+
+# should_comment true but empty body (F15): no post.
+r="$WORK/empty"; mkdir -p "$r"; printf 'low\n' > "$r/severity.txt"; printf 'true\n' > "$r/should_comment.txt"
+: > "$r/comment.md"
+GH_FAKE_LABELS='' run_main "$r"
+eq    "empty comment returns 0"           "$RC" "0"
+lacks "empty comment: no post"            "pr comment"
+
+# Oversized after sanitization (F22): brackets expand ~5x past the cap; no post.
+r="$WORK/big"; mkdir -p "$r"; printf 'low\n' > "$r/severity.txt"; printf 'true\n' > "$r/should_comment.txt"
+{ printf '## x\n'; head -c 20000 /dev/zero | tr '\0' '['; } > "$r/comment.md"
+GH_FAKE_LABELS='' run_main "$r"
+eq    "oversized comment returns 0"       "$RC" "0"
+lacks "oversized comment: no post"        "pr comment"
+
+if [[ "$fail" -ne 0 ]]; then
+  echo "TESTS FAILED"
+  exit 1
+fi
+echo "ALL TESTS PASSED"