fix: support feature branch numbers with 4+ digits

[t-sakoda]

Description

The sequential feature number regex in common.sh and common.ps1 was hardcoded to exactly 3 digits ({3}), causing branches like 1234-feature-name to be rejected once a project exceeds 999 features.

This PR changes the pattern to {3,} (3 or more digits) so that 4+ digit prefixes are recognized correctly. A guard is also added in check_feature_branch / Test-FeatureBranch to prevent malformed timestamps (e.g. 2026031-143022-feat) from being falsely accepted as sequential prefixes.

Closes #344

Testing

• Tested locally with uv run specify --help
• Ran existing tests with uv sync && uv run pytest
• Tested with a sample project (if applicable)

All 27 test_timestamp_branches.py tests pass, including the existing test that rejects partial timestamps.

AI Disclosure

• I did not use AI assistance for this contribution
• I did use AI assistance (describe below)

Code changes generated and reviewed with Claude Code (Claude Opus 4.6).

[Copilot]

Pull request overview

Updates feature-branch parsing in Spec Kit’s Bash and PowerShell helper scripts to support sequential prefixes beyond 999 (3+ digits) while preventing malformed timestamp-like prefixes from being treated as sequential.

Changes:

• Allow sequential feature prefixes with 3+ digits ({3,}) when scanning specs/ and resolving feature directories.
• Update feature-branch validation to accept 4+ digit sequential prefixes.
• Add a guard intended to reject malformed timestamp-like branches (e.g., 2026031-143022-feat) from being accepted as sequential.

Reviewed changes

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

File	Description
scripts/powershell/common.ps1	Expands sequential prefix matching and adds a timestamp-shape guard in Test-FeatureBranch.
scripts/bash/common.sh	Expands sequential prefix matching, updates prefix-based directory resolution, and adds the same timestamp-shape guard in check_feature_branch.

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[Copilot]

Pull request overview

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

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[Copilot]

Pull request overview

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

Comments suppressed due to low confidence (1)

tests/test_timestamp_branches.py:197

• There’s test coverage for rejecting a 7-digit partial date (2026031-143022-feat), but no regression test for the newly-possible case 20260319-143022 (8-digit date + 6-digit time with no final -<slug>). Adding a test that asserts check_feature_branch "20260319-143022" "true" fails would lock in the intended malformed-timestamp guard while still allowing 4+ digit sequential branches.

    def test_accepts_four_digit_sequential_branch(self):
        """check_feature_branch accepts 4+ digit sequential branch."""
        result = source_and_call('check_feature_branch "1234-feat" "true"')
        assert result.returncode == 0

    def test_rejects_partial_timestamp(self):
        """Test 9: check_feature_branch rejects 7-digit date."""
        result = source_and_call('check_feature_branch "2026031-143022-feat" "true"')
        assert result.returncode != 0

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[mnriem]

Please address Copilot feedback

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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[mnriem]

Thank you!