Improve support for sparse cache.

[christian-schilling]

With the addition of a notes backed cache we will have the possibility of avoiding a "cold start" by transferring just the notes to another repo. To keep the amount of extra data small the notes cache is kept sparse: Not all commits have and entry and also in shards by sequence number, as old entries are unlikely to be relevant.
The old traversal logic did not perform very well with sparse cache. Especially "find_known" proved to be a bottleneck. So the traversal is revised now to work better in the sparse cache case.

Change: cache-sparse-shards

[Copilot]

Pull Request Overview

This PR introduces a new :pin filter feature for Josh along with a sequence number caching optimization. The pin filter allows selective tree contents to be "held off" at parent revision versions, useful for temporarily excluding sensitive changes. The sequence number optimization improves cache efficiency by reducing the number of git notes created.

Key changes:

• Implementation of the :pin filter that prevents appearance of selected subtrees for specific revisions
• Addition of sequence number tracking for commits to optimize caching
• Refactored history walking logic to use hide callbacks instead of pre-computing known commits

Reviewed Changes

Copilot reviewed 53 out of 53 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
josh-core/src/filter/mod.rs	Added Op::Pin variant, pin filter application logic, and sequence_number handling
josh-core/src/filter/parse.rs	Added parsing support for :pin filter syntax
josh-core/src/filter/opt.rs	Extended filter optimization functions to handle Pin operations
josh-core/src/cache.rs	Added sequence number computation and encoding/decoding functions; updated cache interface
josh-core/src/cache_notes.rs	Modified to use sequence numbers for selective note storage and path partitioning
josh-core/src/cache_sled.rs	Updated cache backend interface to accept sequence_number parameter
josh-core/src/cache_stack.rs	Updated to propagate sequence_number through cache operations
josh-core/src/history.rs	Refactored walk logic to use hide callbacks; removed find_known function
docs/src/reference/filters.md	Added documentation for the :pin filter
tests/filter/*.t	Updated test expectations to include sequence_number output lines
tests/filter/pin_*.t	Added new test files demonstrating pin filter usage

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[Copilot]

Pull Request Overview

Copilot reviewed 47 out of 47 changed files in this pull request and generated 5 comments.

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[Copilot]

Pull Request Overview

Copilot reviewed 47 out of 47 changed files in this pull request and generated 5 comments.

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