Deduplicate surrogate keys when concatenating with manually-set header

[koriym]

Problem

SurrogateKeys::setSurrogateHeader() applied array_unique() only to the internally generated keys. When the ResourceObject already had a manually-set Surrogate-Key header, the keys were simply concatenated with .=, leaving duplicates between the manual set and the internal set.

This happens when a parent resource and its embedded child share a common tag (e.g. a site-wide purge tag): the child's tag is merged into the internal collection via addTag(), then concatenated with the parent's manually-set header, producing duplicates.

The result is functionally correct — Surrogate-Key is an unordered token set and purging is idempotent, so duplicates never cause wrong purges. But it is an inconsistency (internal keys are deduplicated, the concatenation is not), and the bloat is a latent risk on CDNs that cap header length, where truncation could drop tags and cause purge misses. The more embeds, the larger the header.

Fixes #175

Change

Build the full key set first, then apply array_unique() once, so manual and internal keys are deduplicated consistently. The manual-key-first ordering is preserved (existing testSetSurrogateHeader expectation is unchanged).

Also

Add /.phpunit.cache/ to .gitignore. phpunit.xml.dist uses cacheDirectory=".phpunit.cache", which did not match the stale /.phpunit-cache/ (hyphen) entry, so the cache directory was left untracked.

Checks

• composer cs-fix
• PHPStan + Psalm
• composer test

[koriym]

@coderabbitai review

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📝 Walkthrough

Walkthrough

This PR fixes surrogate key deduplication in SurrogateKeys::setSurrogateHeader(). The method now combines existing manually-set header keys with computed keys, removes duplicates across the merged set, and writes back a normalized result. A new test verifies deduplication works when embedded resources and parent resources share common surrogate tokens. The .gitignore is updated to ignore PHPUnit cache.

Changes

Surrogate Key Deduplication

Layer / File(s)	Summary
Core deduplication logic src/SurrogateKeys.php	setSurrogateHeader() refactored to merge existing header keys and computed surrogate keys, split on spaces, deduplicate the combined set, and write back the normalized space-separated result.
Deduplication test coverage tests/SurrogateKeysTest.php	New test testSetSurrogateHeaderDeduplicatesWithManualKeys() verifies the method does not duplicate shared tokens when combining manually-set headers with child-derived surrogate keys.
Build configuration .gitignore	Added /.phpunit.cache/ to ignore PHPUnit cache artifacts.

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🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	Title accurately describes the main change: deduplicating surrogate keys when concatenating with manually-set headers, which is the primary objective.
Description check	✅ Passed	Description is comprehensive and directly relates to the changeset, explaining the problem, solution, and additional changes to .gitignore.
Linked Issues check	✅ Passed	The PR correctly addresses issue #175 by deduplicating the full surrogate key set (manual + internal) instead of only internal keys, and preserves manual-key-first ordering as expected.
Out of Scope Changes check	✅ Passed	All changes are within scope: surrogate key deduplication logic aligns with #175, test validates the deduplication fix, and .gitignore update matches the phpunit.xml.dist configuration.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-surrogate-key-deduplication

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (41a9b84) to head (4c1c51f).

Additional details and impacted files

@@             Coverage Diff             @@
##                 1.x      #176   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity       246       246           
===========================================
  Files             53        53           
  Lines            750       748    -2     
===========================================
- Hits             750       748    -2     

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🧹 Nitpick comments (1)

.gitignore (1)

10-10: 💤 Low value

Consider removing the stale hyphenated pattern.

Since the PR objectives note that the hyphenated version was "stale" and line 11 now provides the correct pattern matching phpunit.xml.dist, you may want to remove this obsolete entry to avoid confusion.

🧹 Proposed cleanup

-/.phpunit-cache/
 /.phpunit.cache/

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In @.gitignore at line 10, Remove the stale hyphenated .gitignore entry
"/.phpunit-cache/" from the file; locate the obsolete pattern "/.phpunit-cache/"
and delete it so only the corrected pattern (the phpunit.xml.dist-related entry
mentioned in the PR) remains, avoiding redundant/obsolete ignore rules.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In @.gitignore:
- Line 10: Remove the stale hyphenated .gitignore entry "/.phpunit-cache/" from
the file; locate the obsolete pattern "/.phpunit-cache/" and delete it so only
the corrected pattern (the phpunit.xml.dist-related entry mentioned in the PR)
remains, avoiding redundant/obsolete ignore rules.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: a8fe44eb-1b8d-48f1-9e5e-62b72f72908b

📥 Commits

Reviewing files that changed from the base of the PR and between 41a9b84 and 4c1c51f.

📒 Files selected for processing (3)

• .gitignore
• src/SurrogateKeys.php
• tests/SurrogateKeysTest.php