diff --git a/src/cli/stdin-reader.ts b/src/cli/stdin-reader.ts
index 8aeb4c77..04173de8 100644
--- a/src/cli/stdin-reader.ts
+++ b/src/cli/stdin-reader.ts
@@ -1,10 +1,12 @@
 // Stdin reading utility extracted from hook patterns
 // See src/hooks/save-hook.ts for the original pattern
 
-// Timeout for stdin reading - if Claude Code doesn't close stdin within this time,
+// Inactivity timeout for stdin reading - if no data arrives within this time,
 // we parse whatever data we have. This fixes issue #727 where hooks hang at "1/2 done"
 // because stdin.on('end') never fires.
-const STDIN_TIMEOUT_MS = 5000;
+// Using inactivity timeout (reset on each data chunk) instead of absolute timeout
+// to avoid truncating large/slow payloads.
+const STDIN_INACTIVITY_TIMEOUT_MS = 5000;
 
 /**
  * Check if stdin is available and readable.
@@ -24,11 +26,13 @@ function isStdinAvailable(): boolean {
       return false;
     }
 
-    // Check if we can access basic stdin properties without crashing
-    // This triggers Bun's lazy initialization
-    const readable = stdin.readable;
-    return readable !== false;
-  } catch (err) {
+    // Accessing stdin.readable triggers Bun's lazy initialization.
+    // If we get here without throwing, stdin is available.
+    // Note: We don't check the value since Node/Bun don't reliably set it to false.
+    // eslint-disable-next-line @typescript-eslint/no-unused-expressions
+    stdin.readable;
+    return true;
+  } catch {
     // Bun crashed trying to access stdin (EINVAL from fstat)
     // This is expected when Claude Code doesn't provide valid stdin
     return false;
@@ -45,6 +49,7 @@ export async function readJsonFromStdin(): Promise<unknown> {
   return new Promise((resolve, reject) => {
     let input = '';
     let resolved = false;
+    let timeoutId: ReturnType<typeof setTimeout>;
 
     const cleanup = () => {
       try {
@@ -59,6 +64,7 @@ export async function readJsonFromStdin(): Promise<unknown> {
     const resolveWithData = () => {
       if (resolved) return;
       resolved = true;
+      clearTimeout(timeoutId);
       cleanup();
       try {
         resolve(input.trim() ? JSON.parse(input) : undefined);
@@ -67,25 +73,31 @@ export async function readJsonFromStdin(): Promise<unknown> {
       }
     };
 
-    // Timeout handler - resolve with whatever data we have
-    // This fixes issue #727 where stdin.on('end') never fires
-    const timeoutId = setTimeout(() => {
-      if (!resolved) {
-        resolveWithData();
-      }
-    }, STDIN_TIMEOUT_MS);
+    // Reset the inactivity timeout - called on each data chunk
+    const resetTimeout = () => {
+      clearTimeout(timeoutId);
+      timeoutId = setTimeout(() => {
+        if (!resolved) {
+          resolveWithData();
+        }
+      }, STDIN_INACTIVITY_TIMEOUT_MS);
+    };
+
+    // Start initial timeout
+    resetTimeout();
 
     try {
       process.stdin.on('data', (chunk) => {
         input += chunk;
+        // Reset timeout on each data chunk to avoid truncating large/slow payloads
+        resetTimeout();
       });
 
       process.stdin.on('end', () => {
-        clearTimeout(timeoutId);
         resolveWithData();
       });
 
-      process.stdin.on('error', (err) => {
+      process.stdin.on('error', () => {
         if (resolved) return;
         resolved = true;
         clearTimeout(timeoutId);
@@ -94,9 +106,11 @@ export async function readJsonFromStdin(): Promise<unknown> {
         // This is more graceful for hook execution
         resolve(undefined);
       });
-    } catch (err) {
+    } catch {
       // If attaching listeners fails (Bun stdin issue), resolve with undefined
+      resolved = true;
       clearTimeout(timeoutId);
+      cleanup();
       resolve(undefined);
     }
   });