fix(glob,grep): keep exit-code gate at >1 — --no-messages alone is enough

Addresses cubic-dev-ai P1 + P2 findings on #4115.

The original PR relaxed `exitCode > 1` to `> 2` based on the (wrong)
claim that ripgrep exits 2 only on non-fatal I/O issues. ripgrep
actually uses exit code 2 for BOTH fatal errors (pattern syntax,
invalid args) AND non-fatal I/O issues; GNU grep (the fallback backend
in grep/cli.ts) likewise uses 2 for fatal errors. So `> 2` would
silently suppress fatal errors.

The correct fix is just `--no-messages`, which suppresses ripgrep's
stderr only for soft I/O issues (broken symlinks, permission denied)
while leaving fatal-error messages intact. With the gate kept at
`exitCode > 1 && stderr.trim()`:

- Broken symlink: ripgrep exits 2, stderr is empty (suppressed) →
  `stderr.trim()` is falsy → gate fails → partial results survive.
- Fatal error: ripgrep exits 2, stderr has the real error message
  (not suppressed by --no-messages) → gate triggers → error returned.

Reverting both `exitCode > 1` → `> 2` changes; keeping the
`--no-messages` flag additions and the regression test (test comment
updated to describe the cleaner architecture).

Verification: bun test src/tools/glob/ src/tools/grep/ → 30 pass / 0 fail.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/tools/glob/cli.test.ts

@@ -57,8 +57,10 @@ describe("buildRgArgs", () => {
 
   // Regression for #3726: broken/dangling symlinks should not surface as
   // tool errors. --no-messages silences ripgrep's non-fatal stderr warnings
-  // so the downstream "exit code > 2 && stderr.trim()" gate sees a clean
-  // stream when only I/O warnings were emitted.
+  // for I/O issues (broken symlinks, permission denied) without suppressing
+  // fatal-error messages, so the existing "exit code > 1 && stderr.trim()"
+  // gate sees a clean stream for soft I/O issues but still triggers on real
+  // fatal ripgrep errors.
   it("includes --no-messages so broken symlinks do not error the tool (#3726)", () => {
     const args = buildRgArgs({ pattern: "*.ts" })
     expect(args).toContain("--no-messages")