Optimize Dumpster Fire signal with time-based scanning

[erichs]

Remove Rotting Secrets signal (duplicative with Dumpster Fire).

Replace arbitrary entry limits with adaptive time-budget gating:

• Global 8ms time budget shared across parallel directory scans
• Scans as many entries as possible within budget
• Fast systems scan more, slow systems gracefully degrade
• Added context check after expensive stat() syscalls

Performance improvement:

Metric	Before	After
Cold cache time	85ms	<8ms
~/Downloads (716 files)	First 100 entries	All within budget

Files removed:

• src/signals/rotting_secrets.go
• src/signals/rotting_secrets_test.go
• docs/signals/rotting_secrets.md

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 82.85714% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.40%. Comparing base (2d5dc85) to head (67e4828).

Files with missing lines	Patch %	Lines
src/signals/internal/filestat/filestat.go	33.33%	4 Missing ⚠️
src/signals/dumpster_fire.go	92.85%	1 Missing and 1 partial ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #52      +/-   ##
==========================================
- Coverage   81.44%   81.40%   -0.04%     
==========================================
  Files          62       61       -1     
  Lines        4656     4609      -47     
==========================================
- Hits         3792     3752      -40     
+ Misses        672      669       -3     
+ Partials      192      188       -4     

Flag	Coverage Δ
unittests	81.40% <82.85%> (-0.04%)	⬇️

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[Copilot]

Pull request overview

This pull request optimizes the Dumpster Fire signal by replacing arbitrary entry limits with adaptive time-based scanning. The Rotting Secrets signal is removed as it was duplicative with Dumpster Fire.

Changes:

• Removed the Rotting Secrets signal (implementation, tests, and documentation) as it was duplicative with Dumpster Fire
• Implemented parallel directory scanning with a global 8ms time budget for the Dumpster Fire signal
• Changed default scanning configuration from hard entry limits (500 entries, 2ms per directory) to time-based gating (0 entry limit, 0 timeout - uses caller's context)
• Added responsive context checking after expensive stat() syscalls in the scanning loop

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/signals/rotting_secrets.go	Removed duplicative signal implementation
src/signals/rotting_secrets_test.go	Removed tests for deleted signal
docs/signals/rotting_secrets.md	Removed documentation for deleted signal
src/signals/registry.go	Removed Rotting Secrets from signal registry (count: 38 → 37)
SIGNALS.md	Removed Rotting Secrets entry from signals list
README.md	Updated security checks count from 38 to 37
src/signals/internal/filestat/filestat.go	Changed defaults to support time-based gating; added context check after stat() syscall
src/signals/dumpster_fire.go	Implemented parallel scanning with 8ms global time budget

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