diff --git a/bin/install.js b/bin/install.js
index faf23d6e..30bf7742 100755
--- a/bin/install.js
+++ b/bin/install.js
@@ -6786,6 +6786,26 @@ function installSdkIfNeeded() {
     emitSdkFatal('Failed to `npm install -g .` from sdk/.', { globalBin: null, exitCode: 1 });
   }
 
+  // 3a. Explicitly chmod dist/cli.js to 0o755 in the global install location.
+  // `tsc` emits files at process umask (typically 0o644 — non-executable), and
+  // `npm install -g` from a local directory does NOT chmod bin-script targets the
+  // way tarball extraction does. Without this, the `gsd-sdk` bin symlink points at
+  // a non-executable file and `command -v gsd-sdk` fails on every first install
+  // (root cause of #2453). Mirrors the pattern used for hook files in this installer.
+  try {
+    const prefixRes = spawnSync(npmCmd, ['config', 'get', 'prefix'], { encoding: 'utf-8' });
+    if (prefixRes.status === 0) {
+      const npmPrefix = (prefixRes.stdout || '').trim();
+      const sdkPkg = JSON.parse(fs.readFileSync(path.join(sdkDir, 'package.json'), 'utf-8'));
+      const sdkName = sdkPkg.name; // '@gsd-build/sdk'
+      const globalModulesDir = process.platform === 'win32'
+        ? path.join(npmPrefix, 'node_modules')
+        : path.join(npmPrefix, 'lib', 'node_modules');
+      const cliPath = path.join(globalModulesDir, sdkName, 'dist', 'cli.js');
+      try { fs.chmodSync(cliPath, 0o755); } catch (e) { /* Windows / path not found */ }
+    }
+  } catch (e) { /* Non-fatal: PATH verification in step 4 will catch any real failure */ }
+
   // 4. Verify gsd-sdk is actually resolvable on PATH. npm's global bin dir is
   //    not always on the current shell's PATH (Homebrew prefixes, nvm setups,
   //    unconfigured npm prefix), so a zero exit status from `npm install -g`
diff --git a/hooks/gsd-statusline.js b/hooks/gsd-statusline.js
index 9bfbdb1f..11687b97 100755
--- a/hooks/gsd-statusline.js
+++ b/hooks/gsd-statusline.js
@@ -147,10 +147,15 @@ function runStatusline() {
       if (sessionSafe) {
         try {
           const bridgePath = path.join(os.tmpdir(), `claude-ctx-${session}.json`);
+          // used_pct written to the bridge must match CC's native /context reporting:
+          // raw used = 100 - remaining_percentage (no buffer normalization applied).
+          // The normalized `used` value is correct for the statusline progress bar but
+          // inflates the context monitor warning messages by ~13 points (#2451).
+          const rawUsedPct = Math.round(100 - remaining);
           const bridgeData = JSON.stringify({
             session_id: session,
             remaining_percentage: remaining,
-            used_pct: used,
+            used_pct: rawUsedPct,
             timestamp: Math.floor(Date.now() / 1000)
           });
           fs.writeFileSync(bridgePath, bridgeData);
diff --git a/tests/bug-2451-context-monitor-over-report.test.cjs b/tests/bug-2451-context-monitor-over-report.test.cjs
new file mode 100644
index 00000000..6b666890
--- /dev/null
+++ b/tests/bug-2451-context-monitor-over-report.test.cjs
@@ -0,0 +1,185 @@
+/**
+ * Regression test for bug #2451
+ *
+ * The GSD context monitor hook over-reports usage by ~13 percentage points
+ * compared to Claude Code's native /context command. The root cause:
+ *
+ * gsd-statusline.js writes two values to the bridge file:
+ *   - remaining_percentage: raw remaining from CC (e.g. 35%)
+ *   - used_pct: normalized "usable" percentage (e.g. 78%) — accounts for
+ *     the 16.5% autocompact buffer by scaling: (100 - remaining - buffer) /
+ *     (100 - buffer) * 100
+ *
+ * gsd-context-monitor.js displays used_pct (78%) in warning messages.
+ * But CC's native /context shows raw used = 100 - remaining = 65%.
+ * The 13-point gap is exactly the buffer normalization overhead.
+ *
+ * Fix: the bridge must write used_pct as the raw value (Math.round(100 -
+ * remaining)), not the buffer-normalized value. The statusline progress bar
+ * continues to use the normalized value for its own display; only the bridge
+ * value that feeds the context monitor needs to be raw/CC-consistent.
+ */
+
+'use strict';
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const os = require('node:os');
+const path = require('node:path');
+const { execFileSync } = require('node:child_process');
+
+const HOOK_PATH = path.join(__dirname, '..', 'hooks', 'gsd-statusline.js');
+const MONITOR_PATH = path.join(__dirname, '..', 'hooks', 'gsd-context-monitor.js');
+
+/**
+ * Run the statusline hook with a synthetic payload and return the full
+ * bridge JSON object written to /tmp/claude-ctx-{sessionId}.json.
+ */
+function runStatuslineHook(remainingPct, totalTokens = 1_000_000, acwEnv = null) {
+  const sessionId = `test-2451-${Date.now()}-${Math.random().toString(36).slice(2)}`;
+  const payload = JSON.stringify({
+    model: { display_name: 'Claude' },
+    workspace: { current_dir: os.tmpdir() },
+    session_id: sessionId,
+    context_window: {
+      remaining_percentage: remainingPct,
+      total_tokens: totalTokens,
+    },
+  });
+
+  const env = { ...process.env };
+  if (acwEnv != null) {
+    env.CLAUDE_CODE_AUTO_COMPACT_WINDOW = String(acwEnv);
+  } else {
+    delete env.CLAUDE_CODE_AUTO_COMPACT_WINDOW;
+  }
+
+  try {
+    execFileSync(process.execPath, [HOOK_PATH], {
+      input: payload,
+      env,
+      timeout: 4000,
+    });
+  } catch { /* non-zero exit is fine; we only need the bridge file */ }
+
+  const bridgePath = path.join(os.tmpdir(), `claude-ctx-${sessionId}.json`);
+  const bridge = JSON.parse(fs.readFileSync(bridgePath, 'utf-8'));
+  fs.unlinkSync(bridgePath);
+  return bridge;
+}
+
+/**
+ * Run the context monitor hook with a pre-written bridge file and return
+ * the parsed additionalContext string from its stdout.
+ */
+function runMonitorHook(remainingPct, usedPct) {
+  const sessionId = `test-2451-mon-${Date.now()}-${Math.random().toString(36).slice(2)}`;
+  const bridgePath = path.join(os.tmpdir(), `claude-ctx-${sessionId}.json`);
+  fs.writeFileSync(bridgePath, JSON.stringify({
+    session_id: sessionId,
+    remaining_percentage: remainingPct,
+    used_pct: usedPct,
+    timestamp: Math.floor(Date.now() / 1000),
+  }));
+
+  const input = JSON.stringify({ session_id: sessionId, cwd: os.tmpdir() });
+  let stdout = '';
+  try {
+    stdout = execFileSync(process.execPath, [MONITOR_PATH], {
+      input,
+      encoding: 'utf-8',
+      timeout: 5000,
+    });
+  } catch (e) {
+    stdout = e.stdout || '';
+  } finally {
+    try { fs.unlinkSync(bridgePath); } catch { /* noop */ }
+    try { fs.unlinkSync(path.join(os.tmpdir(), `claude-ctx-${sessionId}-warned.json`)); } catch { /* noop */ }
+  }
+
+  if (!stdout) return null;
+  const out = JSON.parse(stdout);
+  return out?.hookSpecificOutput?.additionalContext || null;
+}
+
+// ─── Bridge file used_pct accuracy ──────────────────────────────────────────
+
+describe('bug #2451: bridge used_pct matches CC native reporting', () => {
+  test('used_pct is raw (100 - remaining), not buffer-normalized', () => {
+    // CC reports remaining_percentage=35 → CC native "used" = 100-35 = 65%
+    // Buffer-normalized would give: (100 - (35-16.5)/(100-16.5)*100) ≈ 78%
+    // The bridge used_pct must be 65 (raw), not 78 (normalized).
+    const bridge = runStatuslineHook(35);
+    assert.strictEqual(
+      bridge.used_pct,
+      65,
+      `used_pct should be 65 (raw: 100 - 35) but got ${bridge.used_pct}. ` +
+      'Buffer normalization must NOT be applied to the bridge used_pct, ' +
+      'otherwise context monitor messages over-report usage by ~13 points ' +
+      'compared to CC native /context (root cause of #2451).'
+    );
+  });
+
+  test('used_pct is raw for high remaining (low usage scenario)', () => {
+    // remaining=80 → raw used = 20
+    const bridge = runStatuslineHook(80);
+    assert.strictEqual(bridge.used_pct, 20,
+      `used_pct should be 20 (raw: 100-80) but got ${bridge.used_pct}`);
+  });
+
+  test('used_pct is raw for near-critical remaining', () => {
+    // remaining=20 → raw used = 80
+    const bridge = runStatuslineHook(20);
+    assert.strictEqual(bridge.used_pct, 80,
+      `used_pct should be 80 (raw: 100-20) but got ${bridge.used_pct}`);
+  });
+
+  test('remaining_percentage in bridge matches raw CC value', () => {
+    // The bridge remaining_percentage should be the exact raw value from CC
+    const bridge = runStatuslineHook(42);
+    assert.strictEqual(bridge.remaining_percentage, 42,
+      'bridge remaining_percentage must be the raw CC value (no normalization)');
+  });
+});
+
+// ─── Context monitor message accuracy ───────────────────────────────────────
+
+describe('bug #2451: context monitor warning messages show CC-consistent percentages', () => {
+  test('WARNING message shows raw used_pct consistent with CC reporting', () => {
+    // remaining=30 → raw used=70; bridge stores used_pct=70
+    // Monitor message must say "Usage at 70%", not a buffer-inflated value
+    const msg = runMonitorHook(30, 70);
+    assert.ok(msg, 'hook should emit a warning when remaining=30 (below WARNING_THRESHOLD=35)');
+    assert.match(
+      msg,
+      /Usage at 70%/,
+      `Warning message should say "Usage at 70%" (raw), got: ${msg}`
+    );
+  });
+
+  test('CRITICAL message shows raw used_pct consistent with CC reporting', () => {
+    // remaining=20 → raw used=80
+    const msg = runMonitorHook(20, 80);
+    assert.ok(msg, 'hook should emit a critical warning when remaining=20 (below CRITICAL_THRESHOLD=25)');
+    assert.match(
+      msg,
+      /Usage at 80%/,
+      `Critical message should say "Usage at 80%" (raw), got: ${msg}`
+    );
+  });
+
+  test('gap between hook used_pct and raw CC value is at most 1 (rounding)', () => {
+    // With the fix, the only acceptable deviation is ±1 due to Math.round
+    const rawRemaining = 35;
+    const bridge = runStatuslineHook(rawRemaining);
+    const ccNativeUsed = 100 - rawRemaining; // 65
+    const gap = Math.abs(bridge.used_pct - ccNativeUsed);
+    assert.ok(
+      gap <= 1,
+      `Gap between hook used_pct (${bridge.used_pct}) and CC native used (${ccNativeUsed}) ` +
+      `is ${gap} points — must be ≤1 (rounding). Larger gaps indicate buffer normalization ` +
+      'is still being applied to bridge used_pct (root cause of #2451).'
+    );
+  });
+});
diff --git a/tests/bug-2453-sdk-cli-chmod.test.cjs b/tests/bug-2453-sdk-cli-chmod.test.cjs
new file mode 100644
index 00000000..446342d1
--- /dev/null
+++ b/tests/bug-2453-sdk-cli-chmod.test.cjs
@@ -0,0 +1,88 @@
+/**
+ * Regression test for bug #2453
+ *
+ * installSdkIfNeeded() builds sdk/dist/cli.js via `tsc` then runs
+ * `npm install -g .`. TypeScript emits files at process umask (0o644) and
+ * npm install from a local directory does NOT chmod bin-script targets the
+ * way tarball extraction does. The result: the globally-installed
+ * dist/cli.js lands with mode 644 (non-executable), the `gsd-sdk` symlink
+ * points at a non-executable file, and `command -v gsd-sdk` fails on every
+ * new install.
+ *
+ * Fix: after `npm install -g .`, the installer must explicitly
+ * `chmodSync(cliPath, 0o755)` on the installed dist/cli.js. This mirrors
+ * the pattern already used four times in install.js for hook files.
+ */
+
+'use strict';
+
+const { test, describe } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+
+const INSTALL_SRC = path.join(__dirname, '..', 'bin', 'install.js');
+
+describe('bug #2453: installSdkIfNeeded chmods sdk dist/cli.js to 0o755', () => {
+  let installSrc;
+
+  test('install.js source exists', () => {
+    assert.ok(fs.existsSync(INSTALL_SRC), 'bin/install.js must exist');
+    installSrc = fs.readFileSync(INSTALL_SRC, 'utf-8');
+  });
+
+  test('installSdkIfNeeded contains a chmodSync call for dist/cli.js', () => {
+    installSrc = installSrc || fs.readFileSync(INSTALL_SRC, 'utf-8');
+
+    // Locate the installSdkIfNeeded function body
+    const fnStart = installSrc.indexOf('function installSdkIfNeeded()');
+    assert.ok(fnStart !== -1, 'installSdkIfNeeded function must exist in install.js');
+
+    // Find the end of the function (next top-level function declaration)
+    const fnEnd = installSrc.indexOf('\nfunction ', fnStart + 1);
+    const fnBody = fnEnd !== -1 ? installSrc.slice(fnStart, fnEnd) : installSrc.slice(fnStart);
+
+    // Must chmod dist/cli.js to make it executable after npm install -g .
+    const hasChmod = fnBody.includes('chmodSync') && fnBody.includes('dist/cli.js');
+    assert.ok(
+      hasChmod,
+      'installSdkIfNeeded must call chmodSync on dist/cli.js after npm install -g . ' +
+      '(tsc emits 644; npm does not chmod bin targets from local dir installs — ' +
+      'root cause of #2453: gsd-sdk symlink target is non-executable on first install)'
+    );
+  });
+
+  test('chmodSync for dist/cli.js uses mode 0o755', () => {
+    installSrc = installSrc || fs.readFileSync(INSTALL_SRC, 'utf-8');
+
+    const fnStart = installSrc.indexOf('function installSdkIfNeeded()');
+    const fnEnd = installSrc.indexOf('\nfunction ', fnStart + 1);
+    const fnBody = fnEnd !== -1 ? installSrc.slice(fnStart, fnEnd) : installSrc.slice(fnStart);
+
+    // The chmod call must use 0o755 (executable), not 0o644
+    const has755 = fnBody.includes('0o755') && fnBody.includes('dist/cli.js');
+    assert.ok(
+      has755,
+      'chmodSync for dist/cli.js must use mode 0o755 to make the binary executable'
+    );
+  });
+
+  test('chmodSync appears after npm install -g . step', () => {
+    installSrc = installSrc || fs.readFileSync(INSTALL_SRC, 'utf-8');
+
+    const fnStart = installSrc.indexOf('function installSdkIfNeeded()');
+    const fnEnd = installSrc.indexOf('\nfunction ', fnStart + 1);
+    const fnBody = fnEnd !== -1 ? installSrc.slice(fnStart, fnEnd) : installSrc.slice(fnStart);
+
+    const npmGlobalIdx = fnBody.indexOf("'install', '-g', '.'");
+    const chmodIdx = fnBody.indexOf('chmodSync');
+
+    assert.ok(npmGlobalIdx !== -1, "npm install -g . step must be present in installSdkIfNeeded");
+    assert.ok(chmodIdx !== -1, 'chmodSync must be present in installSdkIfNeeded');
+    assert.ok(
+      chmodIdx > npmGlobalIdx,
+      'chmodSync must appear AFTER the npm install -g . step ' +
+      '(the file to chmod does not exist until npm installs it globally)'
+    );
+  });
+});
diff --git a/tests/gsd-statusline.test.cjs b/tests/gsd-statusline.test.cjs
index 93483445..070e2713 100644
--- a/tests/gsd-statusline.test.cjs
+++ b/tests/gsd-statusline.test.cjs
@@ -255,8 +255,12 @@ describe('context meter respects CLAUDE_CODE_AUTO_COMPACT_WINDOW (#2219)', () =>
   const hookPath = path.join(__dirname, '..', 'hooks', 'gsd-statusline.js');
 
   /**
-   * Run the statusline hook with a synthetic context_window payload and
-   * return the used_pct written to the bridge file.
+   * Run the statusline hook with a synthetic context_window payload.
+   * Returns { normalizedUsed, rawUsedPct } where:
+   *   - normalizedUsed: the buffer-adjusted % shown in the statusline bar
+   *     (parsed from the hook's stdout ANSI output, e.g. "60%")
+   *   - rawUsedPct: the raw value written to the bridge file (100 - remaining,
+   *     CC-consistent per #2451 fix)
    */
   function runHook(remainingPct, totalTokens, acwEnv) {
     const sessionId = `test-2219-${Date.now()}-${Math.random().toString(36).slice(2)}`;
@@ -277,48 +281,70 @@ describe('context meter respects CLAUDE_CODE_AUTO_COMPACT_WINDOW (#2219)', () =>
       delete env.CLAUDE_CODE_AUTO_COMPACT_WINDOW;
     }
 
+    let stdout = '';
     try {
-      execFileSync(process.execPath, [hookPath], {
+      stdout = execFileSync(process.execPath, [hookPath], {
         input: payload,
         env,
+        encoding: 'utf8',
         timeout: 4000,
       });
     } catch (e) {
-      // Non-zero exit is fine — hook exits 0 on success, but we're reading
-      // the bridge file, not the exit code. Ignore exit failures here.
+      stdout = e.stdout || '';
     }
 
+    // Parse normalized used% from the statusline bar output (e.g. "60%")
+    // Strip ANSI escape codes then extract the percentage digit(s) before "%"
+    const clean = stdout.replace(/\x1b\[[0-9;]*m/g, '');
+    const match = clean.match(/(\d+)%/);
+    const normalizedUsed = match ? parseInt(match[1], 10) : null;
+
+    // Read raw used_pct from the bridge file (#2451: bridge stores raw CC value)
     const bridgePath = path.join(os.tmpdir(), `claude-ctx-${sessionId}.json`);
-    const bridge = JSON.parse(fs.readFileSync(bridgePath, 'utf8'));
-    fs.unlinkSync(bridgePath);
-    return bridge.used_pct;
+    let rawUsedPct = null;
+    try {
+      const bridge = JSON.parse(fs.readFileSync(bridgePath, 'utf8'));
+      rawUsedPct = bridge.used_pct;
+      fs.unlinkSync(bridgePath);
+    } catch { /* bridge may not exist if hook exited early */ }
+
+    return { normalizedUsed, rawUsedPct };
   }
 
-  test('default buffer (no env var): 50% remaining → ~60% used', () => {
+  test('default buffer (no env var): 50% remaining → ~60% normalized bar display', () => {
     // Default 16.5% buffer: usableRemaining = (50 - 16.5) / (100 - 16.5) * 100 ≈ 40.12%
-    // used ≈ 100 - 40.12 = 59.88 → rounded 60
-    const used = runHook(50, 1_000_000, null);
-    assert.strictEqual(used, 60);
+    // normalized used ≈ 100 - 40.12 = 59.88 → rounded 60 (shown in statusline bar)
+    const { normalizedUsed } = runHook(50, 1_000_000, null);
+    assert.strictEqual(normalizedUsed, 60);
   });
 
-  test('CLAUDE_CODE_AUTO_COMPACT_WINDOW=400000: 50% remaining → ~83% used', () => {
+  test('CLAUDE_CODE_AUTO_COMPACT_WINDOW=400000: 50% remaining → ~83% normalized bar display', () => {
     // With 1M total, 400k window → buffer = 40%. usableRemaining = (50 - 40) / (100 - 40) * 100 ≈ 16.67%
-    // used ≈ 100 - 16.67 = 83.33 → rounded 83
-    const used = runHook(50, 1_000_000, 400_000);
-    assert.strictEqual(used, 83);
+    // normalized used ≈ 100 - 16.67 = 83.33 → rounded 83 (shown in statusline bar)
+    const { normalizedUsed } = runHook(50, 1_000_000, 400_000);
+    assert.strictEqual(normalizedUsed, 83);
   });
 
   test('CLAUDE_CODE_AUTO_COMPACT_WINDOW=0 falls back to default buffer', () => {
     // Explicit "0" means unset — should behave like no env var (16.5% buffer)
-    const used = runHook(50, 1_000_000, 0);
-    assert.strictEqual(used, 60);
+    const { normalizedUsed } = runHook(50, 1_000_000, 0);
+    assert.strictEqual(normalizedUsed, 60);
   });
 
   test('buffer capped at 100% when ACW exceeds total context', () => {
     // Pathological: ACW > totalCtx → buffer = 100%. With no usable range left,
     // usableRemaining = max(0, (50-100)/(100-100)*100) = max(0, -Inf) = 0,
-    // so used = 100 (context reported as completely full).
-    const used = runHook(50, 1_000_000, 2_000_000);
-    assert.strictEqual(used, 100);
+    // so normalized used = 100 (context reported as completely full in bar).
+    const { normalizedUsed } = runHook(50, 1_000_000, 2_000_000);
+    assert.strictEqual(normalizedUsed, 100);
+  });
+
+  test('bridge used_pct is raw (CC-consistent) regardless of ACW setting (#2451)', () => {
+    // Fix for #2451: bridge used_pct must be raw (100 - remaining), not normalized.
+    // This ensures gsd-context-monitor warning messages match CC native /context.
+    // The ACW normalization only affects the statusline bar display, not the bridge.
+    const { rawUsedPct } = runHook(50, 1_000_000, 400_000);
+    assert.strictEqual(rawUsedPct, 50,
+      'bridge used_pct must be raw (100-50=50) regardless of CLAUDE_CODE_AUTO_COMPACT_WINDOW');
   });
 });