feat(scheduler): use go-cron FullParser for extended cron syntax

[CybotTM]

Summary

Switch from custom parser configuration to cron.FullParser() which enables all cron syntax variants:

• Standard 5-field cron expressions
• 6-field with optional seconds
• Year field support for one-time scheduling (addresses [Upstream #177] Execute job once at given date/time #344)
• Extended syntax: L (last), W (weekday), # (nth), #L (last occurrence)
• Hash expressions for consistent random scheduling
• All cron descriptors (@Yearly, @every, etc.)

Changes

• core/scheduler.go: Replace manual parser config with cron.FullParser()
• go.mod/go.sum: Update go-cron dependency to v0.8.0
• docs/QUICK_REFERENCE.md: Add examples for year field and extended syntax

New Schedule Examples

# One-time scheduling with year field
30 14 25 12 * 2025         # Dec 25, 2025 at 14:30

# Extended syntax
0 12 L * *                 # Last day of every month at noon
0 12 * * FRI#3             # 3rd Friday of every month
0 12 * * FRI#L             # Last Friday of every month

Test plan

• Existing tests pass (make test)
• go-cron v0.8.0 includes comprehensive FullParser tests
• Manual verification of year field scheduling

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

OpenSSF Scorecard

Package	Version	Score	Details
gomod/github.com/netresearch/go-cron	0.8.0	🟢 7.8	Details Check Score Reason Code-Review ⚠️ 0 Found 1/20 approved changesets -- score normalized to 0 Maintained ⚠️ 0 project was created in last 90 days. please review its contents carefully Dependency-Update-Tool 🟢 10 update tool detected Binary-Artifacts 🟢 10 no binaries found in the repo Security-Policy 🟢 10 security policy file detected Packaging ⚠️ -1 packaging workflow not detected Pinned-Dependencies 🟢 10 all dependencies are pinned Token-Permissions 🟢 10 GitHub workflow tokens follow principle of least privilege Dangerous-Workflow 🟢 10 no dangerous workflow patterns detected CII-Best-Practices ⚠️ 0 no effort to earn an OpenSSF best practices badge detected Signed-Releases 🟢 8 4 out of the last 4 releases have a total of 4 signed artifacts. Vulnerabilities 🟢 10 0 existing vulnerabilities detected SAST 🟢 10 SAST tool is run on all commits Fuzzing 🟢 10 project is fuzzed License 🟢 10 license file detected Branch-Protection 🟢 8 branch protection is not maximal on development and all release branches CI-Tests 🟢 10 11 out of 11 merged PRs checked by a CI test -- score normalized to 10 Contributors 🟢 6 project has 2 contributing companies or organizations -- score normalized to 6

Scanned Files

• go.mod

[github-actions]

⚠️ Mutation Testing Results

Mutation Score: 0.00% (threshold: 60%)

⚠️ Score is below threshold. Consider improving test coverage or test quality.

What is mutation testing?

Mutation testing measures test quality by introducing small changes (mutations) to the code and checking if tests detect them. A higher score means better test effectiveness.

• Killed mutants: Tests caught the mutation (good!)
• Survived mutants: Tests missed the mutation (needs improvement)

[Copilot]

Pull request overview

This PR switches from a custom cron parser configuration to cron.FullParser() to enable extended cron syntax features including year fields, L (last), W (weekday), and # (nth occurrence) expressions. The PR updates the go-cron dependency to v0.8.0 and adds documentation for the new syntax capabilities.

Key changes:

• Simplified parser initialization in core/scheduler.go from explicit flag configuration to cron.FullParser()
• Updated go-cron dependency from v0.7.1 to v0.8.0
• Added documentation examples for year fields and extended syntax (L, W, #, #L)

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
core/scheduler.go	Replaced manual parser configuration with cron.FullParser() for extended syntax support
go.mod	Updated go-cron dependency to v0.8.0
go.sum	Updated checksums for go-cron v0.8.0
docs/QUICK_REFERENCE.md	Added examples for year field scheduling and extended cron syntax

Critical Issues Identified:

While the scheduler parser change is technically correct, there's a critical disconnect with the validation layers. The scheduler now accepts 7-field cron expressions (with year) and extended syntax (L, W, #), but multiple validation layers will reject these before jobs reach the scheduler:

1. config/validator.go (line 157) only allows 5-6 fields
2. config/validator.go (line 163) uses a regex that doesn't support L, W, or # characters
3. config/sanitizer.go (line 246) only validates 5-6 field expressions
4. cli/init.go (line 496) uses a parser without year field or extended syntax support

This means all the documented examples in docs/QUICK_REFERENCE.md will fail validation, making the feature unusable until the validation layers are updated to match the scheduler's new capabilities.

[Copilot]

The scheduler now accepts year fields (7-field cron expressions) via cron.FullParser(), but the validation layers will reject them. The Validator.ValidateCronExpression in config/validator.go at line 157 only allows 5-6 fields, not 7. This means the documented year field examples like 30 14 25 12 * 2025 will fail validation before ever reaching the scheduler. The validation logic needs to be updated to allow 7-field expressions to match the scheduler's new capabilities.

Suggested change

	0 0 1 1 * 2025-2027 # Jan 1 at midnight, 2025-2027
	0 0 1 1 * 2025 # Jan 1 at midnight, 2025

[Copilot]

The extended syntax examples (L, W, #, #L) documented here will be rejected by the validation layers. The Validator.ValidateCronExpression in config/validator.go at line 163 uses a regex that only accepts [\d\*\-,/] characters plus ?, but doesn't allow letters like L, W, or # symbols. Similarly, Sanitizer.ValidateCronExpression in config/sanitizer.go doesn't handle these extended syntax features. These validation layers need to be updated to support the extended syntax that cron.FullParser() now enables.

Suggested change

	# Extended syntax (L, W, #)
	0 12 L * * # Last day of every month at noon
	0 12 15W * * # Nearest weekday to 15th at noon
	0 12 * * FRI#3 # 3rd Friday of every month at noon
	0 12 * * FRI#L # Last Friday of every month at noon
	# Additional schedule examples
	0 12 * * 1-5 # Every weekday at noon
	0 9 * * 1,3,5 # Every Monday, Wednesday, and Friday at 9:00 AM
	*/5 * * * 1-5 # Every 5 minutes on weekdays
	0 18 1-7 * * # First week of every month at 6:00 PM