fix(codex): bound hook-expanded prompts

vincentkoc · vincentkoc · commit 3f166b1f6411 · 2026-06-21T07:00:11.000+08:00
diff --git a/extensions/codex/src/app-server/context-engine-projection.test.ts b/extensions/codex/src/app-server/context-engine-projection.test.ts
@@ -279,6 +279,22 @@ describe("projectContextEngineAssemblyForCodex", () => {
     expect(fitted).not.toContain("hook context");
   });
 
+  it("keeps the original input when a hook appends context without a projection", () => {
+    const prompt = "current prompt survives";
+    const hookAppend = `\n\nhook context ${"h".repeat(800)}`;
+    const maxChars = 420;
+
+    const fitted = fitCodexProjectedContextForTurnStart({
+      promptText: `${prompt}${hookAppend}`,
+      preservedRange: { start: 0, end: prompt.length },
+      maxChars,
+    });
+
+    expect(fitted.length).toBeLessThanOrEqual(maxChars);
+    expect(fitted).toContain(prompt);
+    expect(fitted).not.toContain("hook context");
+  });
+
   it("bounds output for a large request under the default Codex turn limit", () => {
     const maxChars = CODEX_TURN_START_TEXT_INPUT_MAX_CHARS;
     // A large assembled header prefix already over the cap forces the
diff --git a/extensions/codex/src/app-server/context-engine-projection.ts b/extensions/codex/src/app-server/context-engine-projection.ts
@@ -122,6 +122,7 @@ export function fitCodexProjectedContextForTurnStart(params: {
   promptText: string;
   contextRange?: CodexProjectedContextRange;
   requestRange?: CodexProjectedContextRange;
+  preservedRange?: CodexProjectedContextRange;
   maxChars?: number;
 }): string {
   const maxChars =
@@ -133,7 +134,19 @@ export function fitCodexProjectedContextForTurnStart(params: {
   }
   const range = normalizeProjectedContextRange(params.contextRange, params.promptText.length);
   if (!range) {
-    return params.promptText;
+    const preservedRange = normalizeProjectedContextRange(
+      params.preservedRange,
+      params.promptText.length,
+    );
+    if (!preservedRange) {
+      return params.promptText;
+    }
+    const preservedText = params.promptText.slice(preservedRange.start, preservedRange.end);
+    if (preservedText.length >= maxChars) {
+      return truncateOlderContext(preservedText, maxChars);
+    }
+    const beforeRange = params.promptText.slice(0, preservedRange.start);
+    return `${truncateOlderContext(beforeRange, maxChars - preservedText.length)}${preservedText}`;
   }
 
   const beforeContext = params.promptText.slice(0, range.start);
diff --git a/extensions/codex/src/app-server/run-attempt.context-engine.test.ts b/extensions/codex/src/app-server/run-attempt.context-engine.test.ts
@@ -540,6 +540,33 @@ describe("runCodexAppServerAttempt context-engine lifecycle", () => {
     await run;
   });
 
+  it("bounds hook-appended prompts without an active context engine", async () => {
+    initializeGlobalHookRunner(
+      createMockPluginRegistry([
+        {
+          hookName: "before_prompt_build",
+          handler: async () => ({ appendContext: `hook context ${"h".repeat(1_100_000)}` }),
+        },
+      ]),
+    );
+    const sessionFile = path.join(tempDir, "session.jsonl");
+    const workspaceDir = path.join(tempDir, "workspace");
+    const harness = createStartedThreadHarness();
+    const params = createParams(sessionFile, workspaceDir);
+    params.prompt = "current prompt survives";
+
+    const run = runCodexAppServerAttempt(params);
+    await harness.waitForMethod("turn/start");
+
+    const inputText = getRequestInputText(harness);
+    expect(inputText.length).toBeLessThanOrEqual(CODEX_TURN_START_TEXT_INPUT_MAX_CHARS);
+    expect(inputText).toContain("current prompt survives");
+    expect(inputText).not.toContain("hook context");
+
+    await harness.completeTurn();
+    await run;
+  });
+
   it("uses configured compaction reserve when sizing Codex context-engine projections", async () => {
     const sessionFile = path.join(tempDir, "session.jsonl");
     const workspaceDir = path.join(tempDir, "workspace");
diff --git a/extensions/codex/src/app-server/run-attempt.ts b/extensions/codex/src/app-server/run-attempt.ts
@@ -1028,6 +1028,26 @@ export async function runCodexAppServerAttempt(
         ? { beforeAgentStartResult: params.beforeAgentStartResult }
         : {}),
     });
+  const resolveShiftedPromptInputRange = (
+    prompt: string,
+    promptInputRange: { start: number; end: number } | undefined,
+    turnPromptText: string,
+  ): CodexProjectedContextRange | undefined => {
+    if (
+      !promptInputRange ||
+      promptInputRange.start < 0 ||
+      promptInputRange.end < promptInputRange.start ||
+      promptInputRange.end > prompt.length ||
+      !turnPromptText.endsWith(prompt)
+    ) {
+      return undefined;
+    }
+    const turnPromptOffset = turnPromptText.length - prompt.length;
+    return {
+      start: turnPromptOffset + promptInputRange.start,
+      end: turnPromptOffset + promptInputRange.end,
+    };
+  };
   const resolveShiftedPromptContextRange = (
     prompt: string,
     promptInputRange: { start: number; end: number } | undefined,
@@ -1095,10 +1115,16 @@ export async function runCodexAppServerAttempt(
       promptBuild.promptInputRange,
       turnPromptText,
     );
+    const preservedRange = resolveShiftedPromptInputRange(
+      promptBuild.prompt,
+      promptBuild.promptInputRange,
+      turnPromptText,
+    );
     return fitCodexProjectedContextForTurnStart({
       promptText: turnPromptText,
       contextRange: projectedRanges?.contextRange,
       requestRange: projectedRanges?.requestRange,
+      preservedRange,
     });
   };
   let codexTurnPromptText = decorateCodexTurnPromptText(promptBuild);
