Fix Slack notify prompt to use literal values, not $VAR (#999)

Claude Code's permission matcher denies any Bash command containing
an unexpanded shell variable (e.g. "$PR_NUMBER"), regardless of
whether the rest of the command matches an allowedTools wildcard
like Bash(gh:*). The prompt told Claude to build its gh command from
env vars using shell expansion, so every attempt was denied no
matter how it was quoted, and Claude burned all 30 turns retrying
variations before timing out.

Interpolate the PR number, repo, URL, and workspace path directly
into the prompt text via GitHub Actions expressions instead, so the
Bash command Claude runs contains literal values with no expansion.
None of these are PR-content-controlled (they come from trusted
event/repository context), so embedding them is safe.

Verified locally: ran the rendered prompt through the claude CLI
with the same allowedTools/model/max-turns and got num_turns=3,
permission_denials=0, and a correct output file.

Co-authored-by: Dan Barr <6922515+danbarr@users.noreply.github.com>

Author: danbarr

.github/workflows/autogen-docs-notify.yml

@@ -102,10 +102,6 @@ jobs:
       # nor make arbitrary network calls (no curl/Bash beyond gh).
       - name: Compose reviewer summary
         uses: anthropics/claude-code-action@51705da45eecce209d4700538bf8377d5b5fc695 # v1.0.152
-        env:
-          PR_NUMBER: ${{ github.event.pull_request.number }}
-          GH_REPO: ${{ github.repository }}
-          PR_URL: ${{ github.event.pull_request.html_url }}
         with:
           anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
           # Skips claude-code-action's OIDC -> GitHub App token exchange
@@ -140,16 +136,11 @@ jobs:
             the `gh` CLI. A later, separate, deterministic step does the
             actual Slack posting.
 
-            Context (available to you as environment variables):
-              PR_NUMBER    - the PR number
-              GH_REPO      - owner/repo of this repository
-              PR_URL       - the PR's html_url
-              MESSAGE_FILE - the path to write the JSON output file to
-              GH_TOKEN     - auth for the `gh` CLI
-
             STEP 1 — Read the PR.
-            Run:
-              gh pr view "$PR_NUMBER" --repo "$GH_REPO" --json title,body,reviewRequests,files,url
+            Run this exact command (the values below are already
+            filled in -- do not substitute shell variables, and do
+            not quote the numbers or the repo name):
+              gh pr view ${{ github.event.pull_request.number }} --repo ${{ github.repository }} --json title,body,reviewRequests,files,url
             From the JSON, extract:
               - the PR title
               - the PR body. The body contains a marker-delimited
@@ -164,16 +155,16 @@ jobs:
                 are GitHub logins).
 
             STEP 2 — Write the message content as JSON.
-            Use the **Write** tool to write a file at the path given by
-            the env var MESSAGE_FILE. The file MUST be valid JSON with
-            EXACTLY this shape:
+            Use the **Write** tool to write a file at exactly this path:
+              ${{ github.workspace }}/.autogen-docs-slack-message.json
+            The file MUST be valid JSON with EXACTLY this shape:
               {
                 "headline": "<one line naming the upstream project/version, plain text>",
                 "summary_bullets": ["...", "..."],
                 "reviewers": [
                   {"login": "<github login>", "note": "<what THIS reviewer should check>"}
                 ],
-                "pr_url": "<the PR url>"
+                "pr_url": "${{ github.event.pull_request.html_url }}"
               }
             Rules:
               - "headline" is plain text only (NO Slack/markdown link
@@ -191,7 +182,7 @@ jobs:
                 have produced any user- or docs-facing changes, which is
                 expected and fine, and in that case their approval simply
                 confirms nothing was missed in the generated docs.
-              - "pr_url" is the value of the PR_URL env var.
+              - "pr_url" must be copied exactly as filled in above.
             Do NOT include any Slack ids, Slack mrkdwn, `<@...>` tags, or
             `<url|text>` links — only the plain content above. Do NOT
             post anything. Do NOT call curl. After writing the file,