[No QA] Embed coding-standards in reviewer subagent prompt for stable prompt caching

.claude/skills/coding-standards/build-reviewer-agent.mjs

@@ -0,0 +1,158 @@
+#!/usr/bin/env node
+/**
+ * build-reviewer-agent.mjs
+ *
+ * Compiles the coding-standards rule files into the code-inline-reviewer
+ * subagent definition, so the full ruleset lives in the subagent's SYSTEM
+ * PROMPT (a cacheable, byte-stable prefix) instead of being pulled in at
+ * runtime via Glob + ~28 Read tool calls (which land in the volatile message
+ * layer and cost orchestration turns every run).
+ *
+ * Design requirements:
+ *  - DETERMINISTIC output: rules sorted by filename, no timestamps, no random
+ *    ids. Same inputs => byte-identical output => stable cache prefix across
+ *    CI runs. This is the whole point — a single non-deterministic byte breaks
+ *    the prompt cache.
+ *  - Emits a checksum of the inputs so cache invalidation on a rules change is
+ *    observable (and intentional).
+ *
+ * Usage:
+ *   node build-reviewer-agent.mjs \
+ *     --rules <dir>        (default: .claude/skills/coding-standards/rules) \
+ *     --template <file>    (default: .claude/skills/coding-standards/code-inline-reviewer.template.md) \
+ *     --out <file>         (default: .claude/agents/code-inline-reviewer.md) \
+ *     --check              (CI mode: fail if --out is stale instead of writing)
+ */
+
+import {readFileSync, writeFileSync, readdirSync, existsSync} from 'node:fs';
+import {createHash} from 'node:crypto';
+import path from 'node:path';
+
+const args = parseArgs(process.argv.slice(2));
+const RULES_DIR = args.rules ?? '.claude/skills/coding-standards/rules';
+const TEMPLATE = args.template ?? '.claude/skills/coding-standards/code-inline-reviewer.template.md';
+const OUT = args.out ?? '.claude/agents/code-inline-reviewer.md';
+const CHECK = Boolean(args.check);
+const DOCS_BASE =
+    'https://github.com/Expensify/App/blob/main/.claude/skills/coding-standards/rules';
+const INJECT_MARKER = '<!-- BUILD:INJECT_RULES -->';
+
+function parseArgs(argv) {
+    const out = {};
+    for (let i = 0; i < argv.length; i++) {
+        const a = argv[i];
+        if (!a.startsWith('--')) continue;
+        const key = a.slice(2);
+        const next = argv[i + 1];
+        if (!next || next.startsWith('--')) {
+            out[key] = true;
+        } else {
+            out[key] = next;
+            i++;
+        }
+    }
+    return out;
+}
+
+function parseFrontmatter(src, filename) {
+    const m = src.match(/^---\n([\s\S]*?)\n---\n?/);
+    const meta = {};
+    if (m) {
+        for (const line of m[1].split('\n')) {
+            const kv = line.match(/^([A-Za-z0-9_-]+):\s*(.*)$/);
+            if (kv) meta[kv[1]] = kv[2].replace(/^["']|["']$/g, '').trim();
+        }
+    }
+    if (!meta.ruleId) {
+        throw new Error(`Rule file ${filename} is missing 'ruleId' in frontmatter`);
+    }
+    if (!meta.title) {
+        throw new Error(`Rule file ${filename} is missing 'title' in frontmatter`);
+    }
+    return meta;
+}
+
+// 1. Read rules, sorted by filename for determinism.
+const ruleFiles = readdirSync(RULES_DIR)
+    .filter((f) => f.endsWith('.md'))
+    .sort();
+
+if (ruleFiles.length === 0) {
+    throw new Error(`No rule files found in ${RULES_DIR}`);
+}
+
+const rules = ruleFiles.map((filename) => {
+    const src = readFileSync(path.join(RULES_DIR, filename), 'utf8');
+    const meta = parseFrontmatter(src, filename);
+    return {
+        filename,
+        slug: filename.replace(/\.md$/, ''),
+        ruleId: meta.ruleId,
+        title: meta.title,
+        body: src.trimEnd(),
+    };
+});
+
+// 2. Build the deterministic ruleId -> docs-link index table.
+const indexRows = rules
+    .map((r) => `| \`${r.ruleId}\` | ${r.title} | [${r.slug}](${DOCS_BASE}/${r.slug}.md) |`)
+    .join('\n');
+
+// 3. Concatenate full rule bodies with stable separators.
+const ruleBlocks = rules
+    .map((r) => `<!-- rule:${r.ruleId} file:${r.filename} -->\n${r.body}`)
+    .join('\n\n---\n\n');
+
+// 4. Checksum the *inputs* (filenames + contents) so a rules change is a
+//    visible, intentional cache-buster — and nothing else moves the bytes.
+const checksum = createHash('sha256')
+    .update(rules.map((r) => `${r.filename}\n${r.body}`).join('\n\n'))
+    .digest('hex')
+    .slice(0, 16);
+
+const injected = [
+    `## Coding Standards (embedded — generated by build-reviewer-agent.mjs)`,
+    ``,
+    `<coding-standards rule-count="${rules.length}" checksum="${checksum}">`,
+    ``,
+    `### Rule index (ruleId → title → docs link)`,
+    ``,
+    `| ruleId | title | docs |`,
+    `| --- | --- | --- |`,
+    indexRows,
+    ``,
+    `### Full rules`,
+    ``,
+    ruleBlocks,
+    ``,
+    `</coding-standards>`,
+].join('\n');
+
+// 5. Inject into the template at the marker.
+const template = readFileSync(TEMPLATE, 'utf8');
+if (!template.includes(INJECT_MARKER)) {
+    throw new Error(`Template ${TEMPLATE} is missing marker ${INJECT_MARKER}`);
+}
+const output = template.replace(INJECT_MARKER, injected) + '\n';
+
+const approxTokens = Math.round(output.length / 4);
+
+// 6. Write or check.
+if (CHECK) {
+    const current = existsSync(OUT) ? readFileSync(OUT, 'utf8') : '';
+    if (current !== output) {
+        console.error(
+            `[build-reviewer-agent] ${OUT} is STALE. Run: node build-reviewer-agent.mjs`,
+        );
+        process.exit(1);
+    }
+    console.error(`[build-reviewer-agent] ${OUT} is up to date (checksum ${checksum}).`);
+} else {
+    writeFileSync(OUT, output);
+    console.error(
+        `[build-reviewer-agent] wrote ${OUT}\n` +
+            `  rules:    ${rules.length}\n` +
+            `  checksum: ${checksum}\n` +
+            `  bytes:    ${output.length} (~${approxTokens} tokens)`,
+    );
+}

.claude/agents/code-inline-reviewer.md → .claude/skills/coding-standards/code-inline-reviewer.template.md

@@ -14,11 +14,12 @@ Your job is to scan through changed files and create **inline comments** for spe
 
 ## Rules
 
-Coding standards are defined as individual rule files in `.claude/skills/coding-standards/rules/`.
+The **complete coding-standards ruleset is embedded in this prompt** under the
+`<coding-standards>` section below. You do NOT need to Glob or Read any rule
+files — every rule, with its reasoning, examples, and Review Metadata (search
+patterns, "DO NOT flag" exceptions), is already in your context.
 
-**Always use the `coding-standards` skill to review changed files.**
-
-Each rule file contains:
+Each embedded rule contains:
 
 - **YAML frontmatter**: `ruleId`, `title`
 - **Reasoning**: Technical explanation of why the rule is important
@@ -27,11 +28,10 @@ Each rule file contains:
 
 ## Instructions
 
-1. **Load all rules:**
-   - Use Glob to list all `.md` files in `.claude/skills/coding-standards/rules/`
-   - Read ALL rule files
-   - Build an explicit checklist of all rules (ruleId + title) from the YAML frontmatter
-   - Build a ruleId-to-filename mapping for creating docs links in comments
+1. **Build your rule checklist from the embedded `<coding-standards>` section.**
+   - The checklist (ruleId + title) and the ruleId-to-docs-link mapping are
+     pre-built for you in the `### Rule index` table at the top of that section.
+   - Do NOT spend turns listing or reading rule files — they are already inlined.
 2. **Get the list of changed files and their diffs:**
    - Use `gh pr diff` to see what actually changed in the PR
    - Focus ONLY on the changed lines, not the entire file
@@ -68,3 +68,5 @@ Use this format for the `body` field of each violation:
 
 <Suggested, specific fix preferably with a code snippet>
 ```
+
+<!-- BUILD:INJECT_RULES -->

.github/workflows/claude-review.yml

@@ -53,6 +53,14 @@ jobs:
         if: steps.set-authorized.outputs.IS_AUTHORIZED == 'true'
         uses: ./.github/actions/composite/setupNode
 
+      # Compile the coding-standards ruleset into the reviewer subagent's
+      # system prompt. Deterministic output (sorted, no timestamps) => the
+      # cached prompt prefix stays byte-stable across runs. Generated on the
+      # fly and gitignored, so the ruleset is never duplicated in source.
+      - name: Generate reviewer agent
+        if: steps.set-authorized.outputs.IS_AUTHORIZED == 'true'
+        run: node .claude/skills/coding-standards/build-reviewer-agent.mjs
+
       - name: Filter paths
         if: steps.set-authorized.outputs.IS_AUTHORIZED == 'true'
         uses: dorny/paths-filter@fbd0ab8f3e69293af611ebaee6363fc25e6d187d # v4.0.1
@@ -90,6 +98,10 @@ jobs:
           claude_args: |
             --model claude-opus-4-6
             --allowedTools "Task,Glob,Grep,Read,Bash(gh pr diff:*),Bash(gh pr view:*),Bash(check-compiler.sh:*)" --json-schema '${{ steps.toolkit.outputs.schema_json }}'
+            --exclude-dynamic-system-prompt-sections
+      # Optional, measure-first: 1h cache TTL. Only net-positive if PR cadence
+      # keeps reviews inside the 1h window; on cold runs it costs 2x write vs 1.25x.
+      #   settings: '{"env":{"ENABLE_PROMPT_CACHING_1H":"1"}}'
 
       - name: Post code review results
         if: |

.gitignore

@@ -180,3 +180,6 @@ server/victory-chart-renderer/.dev/
 
 # Bun lockfiles (VCR uses npm workspaces + package-lock.json; bun is runtime-only)
 bun.lock
+
+# Generated by .claude/skills/coding-standards/build-reviewer-agent.mjs (compiled on the fly in CI)
+.claude/agents/code-inline-reviewer.md