[WIP] Modify cache store to support subdirectory delimiter

[Copilot]

Implementation Complete ✅

Successfully implemented subdirectory delimiter feature for SourceControlCacheStore.

Summary of Changes

Core Implementation:

• Added optional subdirectory_delimiter parameter to split cache keys into hierarchical directory structure
• Each key segment creates a subdirectory named hash(segment) using ActiveSupport::Digest
• Each directory contains _key_chunk file with original segment text
• Value stored in value file in the final directory
• Backward compatible - works without delimiter using original flat structure

Code Quality:

• ✅ Clean separation between simple and subdirectory storage modes
• ✅ Proper error handling throughout
• ✅ Well-documented with comprehensive docstrings
• ✅ Extracted helper method to reduce code duplication
• ✅ Fixed deletion to only remove specific entries, not shared parent directories
• ✅ Uses ActiveSupport::Digest.hexdigest for all hashing (per requirement)

Testing:

• ✅ 36 tests all passing (23 original + 13 new)
• ✅ Comprehensive test coverage including edge cases
• ✅ Verified deletion doesn't affect entries with common prefixes
• ✅ Manual verification confirms correct directory structure

Security:

• ✅ CodeQL scan passed with 0 vulnerabilities

Documentation:

• ✅ Updated README with clear usage examples
• ✅ Documented subdirectory structure and behavior
• ✅ All references updated from SHA256 to ActiveSupport::Digest

Example Usage

cache = ActiveSupport::Cache::SourceControlCacheStore.new(
  cache_path: "/path/to/cache",
  subdirectory_delimiter: "---"
)

cache.write("foo---bar---boo-ba", "27")
# Creates:
# hash(foo)/_key_chunk → hash(bar)/_key_chunk → hash(boo-ba)/_key_chunk + value

Ready for review! 🚀

Original prompt

Modify the cache store so that in its config, it takes a param subdirectory_delimiter. If that is set, it should split the cache key by that delimiter and:

1. Make a subdirectory of the root configured directory for each chunk of the key. The name of each directory should be hash(chunk) using SHA256
2. Put each chunk of the key in a file in the appropriate directory called _key_chunk
3. Put the stored value in a file called value in the final directory. There will be the last _key_chunk too.

Example

• If the delimiter is ---
• The key foo---bar---boo-ba with the value 27 should result in the following file hierarchy

|-- hash(foo)
    |-- _key_chunk (content: "foo")
    |-- hash(bar)
        |-- _key_chunk (content: "bar")
        |-- hash(boo-ba)
            |-- _key_chunk (content: "boo-ba")
            |-- value (content: "27")

Be sure to update specs and README too

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