feat(memory): carve the inert diff types out from behind git-diff

[senamakel]

Why

git-diff gated the whole memory::diff module, so a host that did not want libgit2 in its dependency graph could not so much as name a CrossSourceDiff.

That is more than the feature needs to gate. Of the eleven files under src/memory/diff/, exactly two touch git2:

9  src/memory/diff/ledger.rs
4  src/memory/diff/ledger_helpers.rs
0  everything else

types.rs and source.rs are serde/std-only.

What

pub mod diff is now always compiled.

Ungated	types, source, and their re-exports
Gated on git-diff	ledger + ledger_helpers (touch git2), checkpoint / diff / snapshot (impls written against Ledger), and DiffEngine itself

DiffEngine is gated even though its own declaration is dependency-free: its inherent methods live in the gated modules, so an ungated engine would be a handle with nothing to call.

The distinction is describe vs compute. Without the feature a host can pass a diff around, match on a ChangeKind, and implement SnapshotItemSource; it simply cannot produce one.

Who needs this

A memory-git gate in OpenHuman, whose always-on subconscious memory profile renders CrossSourceDiff and ChangeKind into agent prompts. Stubbing those types host-side instead would mean two definitions of one serde shape, free to drift apart — which is why OpenHuman's own gate guidance says to put a domain's inert types in a dependency-free submodule and gate only behaviour. That gate sheds git2 + libgit2-sys + libz-sys, two of the five remaining native C builds in its kernel profile.

Tests

Two #[cfg(not(feature = "git-diff"))] tests pin the carve-out. The disabled build is the only thing that can catch this regressing — re-gating these types compiles fine with the feature on and only breaks downstream.

They construct and serde-round-trip the types rather than just naming them, so a gated-away derive fails too. The pre-existing types/source unit tests now also run in the disabled build.

Verification

cargo check --no-default-features --features obsidian,persona,sync              # clean
cargo check --no-default-features --features obsidian,persona,sync,git-diff,wiki-git   # clean
cargo test  --no-default-features --features ...,git-diff,wiki-git --lib memory::diff::   # 43 passed
cargo test  --no-default-features --features obsidian,persona,sync --lib memory::diff::  # 14 passed
cargo fmt --all -- --check

Summary by CodeRabbit

• Refactor
  • Improved modularity of memory and diff functionality.
  • Core diff data types remain available when Git-based comparison support is disabled.
  • Git-dependent comparison capabilities are isolated behind an optional feature.
  • Improved compatibility for configurations that do not include Git support.
  • Expanded validation confirms diff data remains serializable and usable across supported configurations.
  • Updated documentation clarifies feature availability and configuration behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 39fcf7d9-5117-4701-8257-144f574cd5ad

📥 Commits

Reviewing files that changed from the base of the PR and between 59e4e00 and be7b395.

📒 Files selected for processing (2)

• src/memory/diff/carve_out_tests.rs
• src/memory/diff/mod.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• src/memory/diff/mod.rs

---

📝 Walkthrough

Walkthrough

The memory diff module keeps types and sources available without git-diff. Git-backed computation, DiffEngine, and related tests require git-diff. Module documentation describes the updated feature boundary.

Changes

Memory diff feature boundary

Layer / File(s)	Summary
Diff gating and compatibility tests src/memory/diff/mod.rs, src/memory/diff/carve_out_tests.rs	Git-dependent imports, modules, and DiffEngine use git-diff gates. Tests cover Git-enabled engine behavior and feature-disabled type serialization and source implementation.
Memory feature-gating documentation src/memory/mod.rs	Documentation describes the partially compiled diff module and the fully gated providers and persona modules.

Estimated code review effort: 2 (Simple) | ~10 minutes

Poem

I’m a rabbit with a tidy diff,
Git sleeps when features drift.
Types still hop from branch to branch,
Sources stay light, tests dance.
DiffEngine wakes when git-diff sings.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes making inert diff types available without the git-diff feature.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

---

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[coderabbitai]

Actionable comments posted: 2

🤖 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.

Inline comments:
In `@src/memory/diff/mod.rs`:
- Around line 140-171: Move the cfg-gated carve_out_tests module from
src/memory/diff/mod.rs into the matching sibling diff_tests.rs file, preserving
both test functions and their imports. Leave only the conditional module
declaration in mod.rs, pointing to the sibling test module, and keep the tests
gated for builds without the git-diff feature.
- Around line 156-159: Update the CrossSourceDiff serialization test to
deserialize the generated json back into a CrossSourceDiff, requiring its
Deserialize implementation, then assert a restored field such as the checkpoint
value matches the original. Keep the existing serialization assertion and
ChangeKind coverage.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: a219b860-1676-458e-9ce4-a2623c6e3c73

📥 Commits

Reviewing files that changed from the base of the PR and between ce98837 and 59e4e00.

📒 Files selected for processing (2)

• src/memory/diff/mod.rs
• src/memory/mod.rs

[tinysweeper]

tinysweeper found nothing blocking. Approving.

             $0.0015 · 18,668 in / 4,980 out · 15,150 cached (81%) · z-ai/glm-5.2
critique:    $0.0005 · 5,033 in  / 1,813 out · 4,318 cached (86%)  · z-ai/glm-5.2
security:    $0.0002 · 4,991 in  / 411 out   · 3,998 cached (80%)  · z-ai/glm-5.2
tests:       $0.0002 · 3,576 in  / 544 out   · 3,021 cached (84%)  · z-ai/glm-5.2
description: $0.0005 · 4,223 in  / 1,914 out · 3,145 cached (74%)  · z-ai/glm-5.2

[tinysweeper]

What this change touches

3 files, +96 -10 across 2 components. The code graph knows nothing about these files yet — normal for newly added files, and a cold index otherwise.

flowchart LR
  n0["src/memory/diff<br/>2 files +81 -1"]:::changed
  n1["src/memory<br/>1 file +15 -9"]:::changed
  classDef changed fill:#0d4429,stroke:#238636,color:#e6edf3
  classDef impacted fill:#161b22,stroke:#6e7681,color:#c9d1d9
  classDef flagged fill:#5a1e02,stroke:#d93f0b,color:#ffffff
  classDef blocking fill:#67060c,stroke:#f85149,color:#ffffff

Loading

_{Green: changed. Grey: untouched, reached through an import or a call. Orange: has findings. Red: has a finding that blocks the merge.}

Component		Files	Lines	Findings
src/memory/diff	changed	2	+81 -1	—
src/memory	changed	1	+15 -9	—

Changed files

src/memory/diff

• src/memory/diff/carve_out_tests.rs
• src/memory/diff/mod.rs

src/memory

• src/memory/mod.rs