Scan for the reworded subagent bullet without a regex; pin setup-bun

CodeQL flagged the fallback line regex as polynomial on crafted prompt
text. A plain line scan does the same match in linear time. setup-bun is
pinned to the v2.2.0 commit.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_012AuVk4nEvBXaTjs4G6wdW4

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: oven-sh/setup-bun@v2
+      - uses: oven-sh/setup-bun@0c5077e51419868618aeaa5fe8019c62421857d6 # v2.2.0
         with:
           bun-version: 1.4.2
       - run: bun install --frozen-lockfile
@@ -26,7 +26,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: oven-sh/setup-bun@v2
+      - uses: oven-sh/setup-bun@0c5077e51419868618aeaa5fe8019c62421857d6 # v2.2.0
         with:
           bun-version: 1.4.2
       - run: bun install --frozen-lockfile

src/interceptors/session-interceptors.ts

@@ -37,8 +37,22 @@ const META_SUBAGENT_OVERTRIGGER =
  * single bullet line telling the model to use `subagent` to save context
  * tokens. Deliberately one line (`[^\n]*`) so nothing else is touched.
  */
-const META_SUBAGENT_OVERTRIGGER_LINE =
-  /^- [^\n]*`subagent` tool[^\n]*context token usage[^\n]*$/m;
+/**
+ * Fallback for a reworded upstream sentence: the bullet line that mentions both
+ * the `subagent` tool and context token usage. A plain line scan (no regex) keeps
+ * this linear on arbitrary prompt text.
+ */
+function replaceSubagentOvertriggerLine(text: string): string | undefined {
+  const lines = text.split("\n");
+  const index = lines.findIndex((line) => {
+    if (!line.startsWith("- ")) return false;
+    const toolAt = line.indexOf("`subagent` tool");
+    return toolAt !== -1 && line.indexOf("context token usage", toolAt) !== -1;
+  });
+  if (index === -1) return undefined;
+  lines[index] = CALIBRATED_SUBAGENT_RULE;
+  return lines.join("\n");
+}
 
 const CALIBRATED_SUBAGENT_RULE =
   "- Perform routine file reads (`read`, `file_hash_read`, `file_outline`), targeted searches (`grep`, `glob`, `ast_structural_search`, `symbol_references`), and dependency checks (`repo_map`, `blast_radius`) directly in the main context. Only spawn a `subagent` when broad exploration spans more than 8 files or when executing independent parallel workstreams.";
@@ -64,11 +78,14 @@ export function calibrateSystemPromptInPlace(
     if (text.includes(META_SUBAGENT_OVERTRIGGER)) {
       text = text.replace(META_SUBAGENT_OVERTRIGGER, CALIBRATED_SUBAGENT_RULE);
       modified = true;
-    } else if (META_SUBAGENT_OVERTRIGGER_LINE.test(text)) {
+    } else {
       // Upstream reworded the sentence: still replace the whole bullet line so
       // the calibration does not silently become a no-op.
-      text = text.replace(META_SUBAGENT_OVERTRIGGER_LINE, CALIBRATED_SUBAGENT_RULE);
-      modified = true;
+      const replaced = replaceSubagentOvertriggerLine(text);
+      if (replaced !== undefined) {
+        text = replaced;
+        modified = true;
+      }
     }
     const overlay = buildMuseSystemOverlay();
     if (!text.includes("<muse-1.3-harness-calibration>")) {