[BUG] Grep count mode shows contradictory output when searching a single file

Summary

When using the Grep tool with output_mode="count" on a single file, the output shows contradictory information - the count is displayed correctly, but the summary line incorrectly shows "0 total occurrences across 0 files".

Environment

• Product: Claude Code / Cowork
• Version: Claude for Mac 1.0.3218 (8679c9)
• Tool: Grep

Steps to Reproduce

1. Create a test file:

echo -e "Line 1\nLine 2\nLine 3\nLine 4\nLine 5" > /tmp/test.txt

1. Use Grep with count mode on the single file:

Grep(pattern="Line", path="/tmp/test.txt", output_mode="count")

Actual Output

5

Found 0 total occurrences across 0 files.

Expected Output

5

Found 5 total occurrences across 1 file.

Or alternatively:

/tmp/test.txt:5

Found 5 total occurrences across 1 file.

Additional Context

Searching a directory works correctly:

Grep(pattern="Line", path="/tmp", output_mode="count")

Output:
/tmp/test.txt:5

Found 5 total occurrences across 1 file.  ← Correct!

The issue only occurs when searching a single file directly, not when searching a directory.

Impact

• User confusion: The output contradicts itself (shows count but says 0 occurrences)
• Script parsing issues: Automated tools parsing grep output may get incorrect results
• Trust: Contradictory output may cause users to question tool reliability

Suggested Fix

Update the count aggregation logic to correctly handle single-file searches, ensuring the summary line matches the actual count displayed.

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Additional test cases that reproduce the issue:

# Test 1: Any pattern
Grep(pattern=".", path="/tmp/test.txt", output_mode="count")
→ Shows count, but "Found 0 total occurrences across 0 files"

# Test 2: Regex pattern  
Grep(pattern="Line [0-9]+", path="/tmp/test.txt", output_mode="count")
→ Shows count, but "Found 0 total occurrences across 0 files"

# Test 3: No matches (works correctly)
Grep(pattern="NONEXISTENT", path="/tmp/test.txt", output_mode="count")
→ "No matches found" (correct behavior)