[codex] Inject LSP diagnostics context

README.md

@@ -10,7 +10,7 @@ Codex plugin that ports the standalone LSP runtime from [`pi-lsp-client`](https:
 |------|--------|
 | `apply_patch` succeeds | parses `tool_input.command`, extracts added/updated/moved files, and checks each with LSP error diagnostics |
 | `write` / `edit` / `multiedit` succeeds | checks `path`, `filePath`, or `file_path` aliases |
-| diagnostics contain errors | returns Codex `PostToolUse` blocking feedback so Codex fixes the file |
+| diagnostics contain errors | returns Codex `PostToolUse` blocking feedback and injects the same diagnostics as additional context so Codex fixes the file |
 | no diagnostics | emits no hook output |
 | unsupported extension | emits no hook output |
 | missing configured language server | surfaces the install/config message through hook or MCP output |

src/codex-hook.ts

@@ -15,6 +15,15 @@ interface DiagnosticBlock {
 	diagnostics: string;
 }
 
+interface PostToolUseHookOutput {
+	decision: "block";
+	reason: string;
+	hookSpecificOutput: {
+		hookEventName: "PostToolUse";
+		additionalContext: string;
+	};
+}
+
 const MUTATION_TOOL_NAMES = new Set(["apply_patch", "write", "edit", "multiedit", "multi_edit"]);
 const CLEAN_DIAGNOSTICS_TEXT = "No diagnostics found";
 const UNSUPPORTED_EXTENSION_TEXT = "No LSP server configured for extension:";
@@ -43,7 +52,15 @@ export async function runLspPostToolUseHook(
 	const reason = blocks
 		.map(({ filePath, diagnostics }) => `LSP diagnostics after editing ${filePath}:\n${diagnostics}`)
 		.join("\n\n");
-	return `${JSON.stringify({ decision: "block", reason })}\n`;
+	const output: PostToolUseHookOutput = {
+		decision: "block",
+		reason,
+		hookSpecificOutput: {
+			hookEventName: "PostToolUse",
+			additionalContext: reason,
+		},
+	};
+	return `${JSON.stringify(output)}\n`;
 }
 
 export function extractMutatedFilePaths(input: CodexPostToolUseInput): string[] {

test/codex-hook.test.ts

@@ -51,12 +51,72 @@ describe("codex PostToolUse hook", () => {
 
 		expect(JSON.parse(output)).toEqual({
 			decision: "block",
+			hookSpecificOutput: {
+				hookEventName: "PostToolUse",
+				additionalContext:
+					"LSP diagnostics after editing src/broken.ts:\n" +
+					"error[typescript] (2304) at 1:1: Cannot find name 'missing'.",
+			},
 			reason:
 				"LSP diagnostics after editing src/broken.ts:\n" +
 				"error[typescript] (2304) at 1:1: Cannot find name 'missing'.",
 		});
 	});
 
+	it("injects only files with diagnostics when multiple files are edited", async () => {
+		const checkedFilePaths: string[] = [];
+		const output = await runLspPostToolUseHook(
+			{
+				tool_name: "MultiEdit",
+				tool_input: {
+					file_paths: ["src/clean.ts", "README.md", "src/broken.ts", "src/broken.ts"],
+				},
+				tool_response: { ok: true },
+			},
+			async (filePath) => {
+				checkedFilePaths.push(filePath);
+				if (filePath === "src/broken.ts") {
+					return "error[typescript] (2322) at 1:7: Type 'number' is not assignable to type 'string'.";
+				}
+				if (filePath === "README.md") {
+					return "No LSP server configured for extension: .md";
+				}
+				return "No diagnostics found";
+			},
+		);
+
+		const expectedDiagnostics =
+			"LSP diagnostics after editing src/broken.ts:\n" +
+			"error[typescript] (2322) at 1:7: Type 'number' is not assignable to type 'string'.";
+
+		expect(checkedFilePaths).toEqual(["src/clean.ts", "README.md", "src/broken.ts"]);
+		expect(JSON.parse(output)).toEqual({
+			decision: "block",
+			hookSpecificOutput: {
+				hookEventName: "PostToolUse",
+				additionalContext: expectedDiagnostics,
+			},
+			reason: expectedDiagnostics,
+		});
+	});
+
+	it("does not run diagnostics for failed mutation tool responses", async () => {
+		const output = await runLspPostToolUseHook(
+			{
+				tool_name: "apply_patch",
+				tool_input: {
+					command: "*** Begin Patch\n*** Update File: src/broken.ts\n@@\n+missing();\n*** End Patch\n",
+				},
+				tool_response: { isError: true },
+			},
+			async () => {
+				throw new Error("diagnostics should not run after failed mutations");
+			},
+		);
+
+		expect(output).toBe("");
+	});
+
 	it("is silent for clean diagnostics and unsupported extensions", async () => {
 		const output = await runLspPostToolUseHook(
 			{