Fix error handling in boss-mode report generation to surface I/O errors

[Copilot]

Boss-mode report generation silently fell back to the full LLM pipeline on any file read error, including permission/I/O failures. This masked real errors and wasted tokens.

Changes

• Error handling: Explicitly check for os.IsNotExist vs other errors
  • File not found → log and continue to full pipeline (expected)
  • Permission/I/O errors → surface to user and abort (unexpected)

// Before: all errors treated as "file doesn't exist"
if content, readErr := os.ReadFile(teamReportPath); readErr == nil && len(content) > 0 {
    // use shortcut
}
log.Printf("no existing team report found, running full pipeline")

// After: distinguish expected from unexpected errors
content, readErr := os.ReadFile(teamReportPath)
if readErr != nil {
    if !os.IsNotExist(readErr) {
        log.Printf("Error reading team report file %s: %v", teamReportPath, readErr)
        postEphemeral(api, cmd, fmt.Sprintf("Error reading team report file: %v", readErr))
        return
    }
    log.Printf("no existing team report found, running full pipeline")
} else if len(content) > 0 {
    // use shortcut
}

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[Copilot]

Pull request overview

This PR improves error handling in boss-mode report generation to properly distinguish between expected file-not-found errors and unexpected I/O or permission errors. Previously, all file read errors were silently treated as "file doesn't exist", which masked real problems and wasted LLM tokens by falling back to the full pipeline unnecessarily.

Changes:

• Refactored error handling for team report file reads to explicitly check os.IsNotExist and surface unexpected errors to users
• Updated go.mod to move github.com/robfig/cron/v3 from indirect to direct dependency (already directly imported in auto_fetch.go)

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
slack.go	Improved error handling in handleGenerateReport to distinguish file-not-found from I/O/permission errors, surfacing unexpected errors instead of silently falling back
go.mod	Correctly moved robfig/cron/v3 from indirect to direct dependency status

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Consider adding an else clause to log when the team report file exists but is empty. Currently, this case falls through to the full pipeline silently, while the file-not-found case logs "no existing team report found, running full pipeline". For consistency and debuggability, empty files should also be logged, e.g., "generate-report boss: team report file is empty, running full pipeline".

Suggested change

	} else if len(content) > 0 {
	} else if len(content) == 0 {
	// File exists but is empty - fall through to full pipeline below
	log.Printf("generate-report boss: team report file is empty, running full pipeline")
	} else {