feat: add basic prompt submit hook (#694)

hooks/prompt-instructions.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+# UserPromptSubmit hook - adds instructions to every prompt
+# Reads JSON from stdin, outputs instructions to stdout, exits 0
+
+# Consume stdin (required for hook protocol)
+cat > /dev/null
+
+# Output instructions that will be injected into agent context
+echo "Be specific. Double check your work. Ask clarifying questions."
+
+exit 0

src/cli/App.tsx

@@ -4522,6 +4522,12 @@ export default function App({
         return { submitted: false };
       }
 
+      // Capture successful hook feedback to inject into agent context
+      const userPromptSubmitHookFeedback =
+        hookResult.feedback.length > 0
+          ? `${SYSTEM_REMINDER_OPEN}\n${hookResult.feedback.join("\n")}\n${SYSTEM_REMINDER_CLOSE}`
+          : "";
+
       // Capture the generation at submission time, BEFORE any async work.
       // This allows detecting if ESC was pressed during async operations.
       const submissionGeneration = conversationGenerationRef.current;
@@ -6433,7 +6439,7 @@ ${SYSTEM_REMINDER_CLOSE}
         lastNotifiedModeRef.current = currentMode;
       }
 
-      // Combine reminders with content (session context first, then permission mode, then plan mode, then ralph mode, then skill unload, then bash commands, then memory reminder)
+      // Combine reminders with content (session context first, then permission mode, then plan mode, then ralph mode, then skill unload, then bash commands, then hook feedback, then memory reminder)
       const allReminders =
         sessionContextReminder +
         permissionModeAlert +
@@ -6441,6 +6447,7 @@ ${SYSTEM_REMINDER_CLOSE}
         ralphModeReminder +
         skillUnloadReminder +
         bashCommandPrefix +
+        userPromptSubmitHookFeedback +
         memoryReminderContent;
       const messageContent =
         allReminders && typeof contentParts === "string"

src/hooks/executor.ts

@@ -275,6 +275,19 @@ export async function executeHooks(
     const result = await executeHookCommand(hook, input, workingDirectory);
     results.push(result);
 
+    // Collect feedback from stdout when hook succeeds (exit 0)
+    // Only for UserPromptSubmit and SessionStart hooks
+    if (result.exitCode === HookExitCode.ALLOW) {
+      if (
+        result.stdout?.trim() &&
+        (input.event_type === "UserPromptSubmit" ||
+          input.event_type === "SessionStart")
+      ) {
+        feedback.push(result.stdout.trim());
+      }
+      continue;
+    }
+
     // Collect feedback from stderr when hook blocks
     // Format: [command]: {stderr} per spec
     if (result.exitCode === HookExitCode.BLOCK) {