feat: add stdin support for CLI using temp-file approach

[mvance]

Summary

This PR adds stdin support to the summarize CLI, allowing users to pipe content directly into the tool using - as the input argument. This is particularly useful for summarizing clipboard content and integrating with shell workflows.

Changes

Core Implementation

• Extended InputTarget type to include { kind: 'stdin' } in src/content/asset.ts
• Added stdin resolution in resolveInputTarget() to recognize - (including surrounding whitespace) as stdin input
• Implemented stdin processing in runCli() using temp-file approach:
  • Reads stdin content into a temporary file with secure permissions (0o600)
  • Processes via existing handleFileInput logic to minimize code duplication
  • 50MB size limit to prevent memory issues
  • Automatic cleanup in finally block
  • Uses injected stdin from RunEnv (falls back to process.stdin)
• Updated help text to document stdin support in argument descriptions and examples

Error Handling

• Clear error for empty stdin: "Stdin is empty"
• Clear error for oversized input: "Stdin content exceeds maximum size of 50.0MB"
• Clear error for --extract with stdin: "--extract is not supported for piped stdin input"
• Updated error for --markdown-mode restrictions with better messaging

Documentation

• Updated README.md with stdin section including examples and 50MB size limit note
• Added stdin examples to both rich and concise help text
• Focused examples on practical use case: pbpaste | summarize -

Testing

• Added comprehensive stdin resolution tests in tests/input.resolve-input-target.test.ts
• Created new tests/cli.stdin.test.ts with 6 tests covering:
  • Empty stdin handling (completely empty and whitespace-only)
  • --extract flag rejection with stdin
  • --markdown-mode llm allowance for stdin
  • --markdown-mode readability rejection for stdin
  • Basic stdin processing without errors
• All tests pass (39 total across related test suites)

Usage Examples

# Summarize clipboard content
pbpaste | summarize -

# Pipe command output
echo "Meeting notes..." | summarize -

# With options
pbpaste | summarize - --length short

Technical Details

• Temp file approach: Reuses existing handleFileInput logic, minimizing changes and maintaining consistency
• Size limit: 50MB maximum to prevent OOM issues
• Security: Temp files created with 0o600 permissions
• Cleanup: Automatic removal in finally block prevents temp file accumulation
• Unix convention: Uses standard - to represent stdin
• Compatibility: No breaking changes; existing file and URL inputs work unchanged

Performance

• Streaming size check prevents loading oversized content into memory
• Efficient Buffer handling with minimal copying
• Random filename suffix prevents collisions

Future Enhancements

This PR lays groundwork for future transcript markdown formatting support via --markdown-mode llm for stdin/file inputs.

Verification

• ✅ All existing tests pass (no regressions)
• ✅ New tests added and passing
• ✅ Build compiles successfully
• ✅ Linting passes (0 errors)
• ✅ Manual testing confirms proper behavior

CI Status Note

The extension-e2e test failures shown in CI are pre-existing flaky tests that are also failing on the main branch. These failures are unrelated to the stdin support changes in this PR. The extension E2E tests involve Chrome browser automation that is sensitive to timing and environment conditions.

All relevant unit tests pass successfully:

• test (22): ✅ Pass
• test (24): ✅ Pass
• GitGuardian Security Checks: ✅ Pass

Related

This implements stdin support using the temp-file approach, which keeps the implementation simple while enabling powerful shell integration workflows.