---
name: audit ambiguous paths followup
overview: Production audit of the ambiguous-paths branch against origin/master. Documents critical round-trip issues, approved fixes, accepted limitations, and required regression tests for implementation in a follow-up Agent-mode session.
todos:
  - id: fix-metadata-drift
    content: "Fix 1: Update dedup cleanup rename flow to keep tree metadata/path indexes in sync"
    status: completed
  - id: fix-batch-removal-dedup
    content: "Fix 2: Exclude co-removed siblings from dedup cleanup sibling enumeration"
    status: completed
  - id: fix-added-paths
    content: "Fix 3: Extend added_paths in api.rs to include middleware extension and dedup suffix"
    status: completed
  - id: fix-ref-path-final
    content: "Fix 4: Complete Phase 2 of previous audit Fix 3 -- pass final_paths to collect_referents instead of global text rewrite"
    status: completed
  - id: fix-regression-tests
    content: "Fix 5: Add regression tests for Fixes 1-4"
    status: completed
isProject: false
---

# Ambiguous Paths Audit Fix Plan

> This plan was generated by `/audit` from a Plan-mode session.
> Refer to `.cursor/rules/atlas.mdc` for full project standards.

## Standards

These standards govern every fix in this plan. An implementer MUST read `.cursor/rules/atlas.mdc` before starting.

### Round-Trip Identity (from `atlas.mdc` §Quality Standard)

Syncback (or two-way sync) writes a directory tree. Building an rbxl from that directory tree and forward-syncing it back must produce a bit-identical instance tree -- same names, same classes, same properties, same hierarchy, same ref targets. Any deviation is a bug.

### CLI Syncback Parity (from `atlas.mdc` §Two-Way Sync Strategy)

Plugin-based sync must produce exactly the same filesystem output that `atlas syncback` would give for the same input. Byte-for-byte identical files, identical directory structures, identical naming. Any divergence is a bug until proven otherwise.

### Code Quality (from `atlas.mdc` §Code Quality Standard)

DRY code that is easy to reason about and hard to get wrong. Small helper refactors are in scope; major pipeline redesign is deferred.

## Context

Audited branch `ambiguous-paths` against `origin/master` using commit range `origin/master..HEAD`.

Primary findings:

- Critical path drift in dedup cleanup rename flow (`[src/change_processor.rs](d:/UserGenerated/rojo/src/change_processor.rs)`).
- Critical batch-removal dedup cleanup counts co-removed siblings as "remaining", defeating group-to-1 cleanup (`[src/change_processor.rs](d:/UserGenerated/rojo/src/change_processor.rs)`).
- Critical same-batch Ref target path synthesis mismatch for added instances (`[src/web/api.rs](d:/UserGenerated/rojo/src/web/api.rs)`).
- Critical ref-path post-processing strategy relies on global text replacement (`[src/syncback/mod.rs](d:/UserGenerated/rojo/src/syncback/mod.rs)`, `[src/syncback/fs_snapshot.rs](d:/UserGenerated/rojo/src/syncback/fs_snapshot.rs)`).
- Known limitation accepted for this release: duplicate-named children under ProjectNode currently skipped in `[src/snapshot_middleware/project.rs](d:/UserGenerated/rojo/src/snapshot_middleware/project.rs)`.
- Known limitation accepted for this release: greedy matcher is not globally optimal (`[src/snapshot/matching.rs](d:/UserGenerated/rojo/src/snapshot/matching.rs)`, `[src/syncback/matching.rs](d:/UserGenerated/rojo/src/syncback/matching.rs)`, `[plugin/src/Reconciler/matching.lua](d:/UserGenerated/rojo/plugin/src/Reconciler/matching.lua)`).

## Fixes

Each fix below was approved by the user during the audit quiz. Implement in order.

### Fix 1: Keep tree metadata consistent after dedup cleanup rename

- **Status:** Approved
- **Finding:** Step 2d / Step 8 (rename/delete interactions + VFS suppression)
- **Files:** `[src/change_processor.rs](d:/UserGenerated/rojo/src/change_processor.rs)`
- **Problem:** In dedup cleanup (`~1073-1203`), the code renames files (`fs::rename`) and suppresses both old/new paths, but does not update the renamed sibling's `InstigatingSource::Path` or metadata path indexes. Subsequent writes can target stale paths.
- **Solution:** After successful `DedupCleanupAction::RemoveSuffix` / `PromoteLowest`, locate the sibling instance being renamed, update its metadata source path and relevant path indexes in-memory, and keep suppression counters consistent with the updated path.
- **Risk:** Medium; touches tree mutation bookkeeping and rename lifecycle.
- **Verify round-trip:** Create duplicate siblings (`Foo`, `Foo~1`), delete `Foo`, ensure `Foo~1 -> Foo` rename occurs, then issue a property update to the survivor in same session and verify disk write targets new path and survives rebuild.
- **Verify syncback parity:** Compare output of two-way deletion flow to CLI syncback on equivalent tree state; both must produce the same remaining filename/meta layout.
- **Tests required:**
  - Rust integration test in `[tests/tests/two_way_sync.rs](d:/UserGenerated/rojo/tests/tests/two_way_sync.rs)` covering delete-triggered dedup cleanup followed by update.
  - Optional focused unit test around cleanup metadata path update helper in `[src/change_processor.rs](d:/UserGenerated/rojo/src/change_processor.rs)`.

### Fix 2: Exclude co-removed siblings from dedup cleanup sibling enumeration

- **Status:** Approved
- **Files:** `[src/change_processor.rs](d:/UserGenerated/rojo/src/change_processor.rs)`
- **Problem:** In the dedup cleanup loop (lines 1077-1203), the sibling enumeration (line 1120) only skips `sibling_ref == removed_id` -- the single instance being processed in the current iteration. It does NOT skip other instances that are also in `patch_set.removed_instances`. When multiple siblings from the same dedup group are removed in a single patch, the co-removed instances are incorrectly counted as "remaining", inflating the sibling count and defeating cleanup rules.
- **Failure path:** Remove `Foo` (A) and `Foo~1` (B) from a group of 3, leaving `Foo~2` (C) as the sole survivor. api.rs deletes all files first. In the dedup cleanup loop, iteration for A finds B and C as remaining (count=2), so group-to-1 does not fire; instead `PromoteLowest` tries to rename the already-deleted `Foo~1` → `Foo` (fails). Iteration for B finds A and C as remaining (count=2), group-to-1 again does not fire. Result: C keeps its `~2` suffix permanently when it should have been renamed to `Foo`.
- **Solution:** Before the dedup cleanup loop, build a `HashSet<Ref>` from `patch_set.removed_instances`. In the sibling enumeration (line 1121), change the skip condition from `sibling_ref == removed_id` to `removed_set.contains(&sibling_ref)`:

```rust
let removed_set: HashSet<Ref> = patch_set.removed_instances.iter().copied().collect();

// ... inside sibling loop:
for &sibling_ref in parent_inst.children() {
    if removed_set.contains(&sibling_ref) {
        continue;
    }
    // ... rest of sibling processing
}
```

- **Risk:** Low; narrow, mechanical change. The HashSet construction is O(n) and the lookup is O(1).
- **Verify round-trip:** Remove 2 of 3 duplicate siblings via two-way sync. Verify the sole survivor has its dedup suffix removed and survives rebuild with the clean name.
- **Verify syncback parity:** N/A (dedup cleanup is a two-way sync operation only).
- **Tests required:**
  - Rust integration test in `[tests/tests/two_way_sync.rs](d:/UserGenerated/rojo/tests/tests/two_way_sync.rs)`: batch-remove 2 of 3 same-named siblings, verify survivor is renamed from `Foo~2` to `Foo`.
  - Edge test: batch-remove ALL members of a dedup group (no survivor); verify no spurious rename attempts.

### Fix 3: Build correct same-batch added Ref paths

- **Status:** Approved
- **Lineage:** Extends `ambiguous_paths_audit_fixes_9d3ed6da` Fix 2 (completed), which replaced `escape_ref_path_segment` with `slugify_name` in `added_paths` but explicitly acknowledged the missing extension as a limitation. The current code at lines 637-641 of `api.rs` uses `slugify_name`; this fix adds the remaining segments.
- **Finding:** Step 2a / Step 10 (plugin->server wire format and write processing)
- **Files:** `[src/web/api.rs](d:/UserGenerated/rojo/src/web/api.rs)`
- **Problem:** `added_paths` map (`~622-649`) uses only slugified instance name (from the previous fix); it still omits middleware extension and dedup suffix. `syncback_updated_properties` then writes incorrect `Rojo_Ref_`* when target is newly added in same request (`~2694-2706`).
- **Solution:** Extend the existing `added_paths` builder (lines 637-649) to derive the full filesystem name: slugified name + middleware extension based on `added.class_name` and `added.children.is_empty()` + dedup suffix if colliding with siblings. Reuse `tentative_fs_name` logic from `ref_properties.rs` or the shared helper from the Deferred Refactors section.
- **Risk:** Medium; affects same-request Ref persistence edge path.
- **Verify round-trip:** Send `/api/write` with add(target script/model) + update(ref property pointing to target) in one batch; verify persisted path includes correct segment (`.server.luau`, `.model.json5`, or dedup suffix) and resolves after rebuild.
- **Verify syncback parity:** Run equivalent scenario via CLI syncback fixture and compare written `Rojo_Ref_`* attribute string.
- **Tests required:**
  - Rust integration test in `[tests/tests/two_way_sync.rs](d:/UserGenerated/rojo/tests/tests/two_way_sync.rs)` for same-batch add+ref on file-backed and directory-backed targets.
  - Edge test for dedup suffix target (e.g., `Foo~1`).

### Fix 4: Complete attribute-scoped final paths (previously incomplete)

- **Status:** Approved
- **Finding:** Step 2a / Step 9 / Step 11h (round-trip identity, parity, determinism)
- **Lineage:** `ambiguous_paths_audit_fixes_9d3ed6da` Fix 3 defined a two-phase fix. Phase 1 (correct misleading comment) was completed -- visible at lines 194-199 of `ref_properties.rs`. Phase 2 (pass `final_paths` to `collect_referents`) was NOT completed despite the todo being marked "completed". The API was prepared (`final_paths: Option<&HashMap<Ref, String>>` parameter exists at line 188 of `ref_properties.rs`) but the call site at line 177 of `mod.rs` still passes `None`. The `ref_path_map` infrastructure was built by `ref_path_and_dedup_integration_81a47dfe` and is populated during the syncback walk (used at lines 614-637 of `mod.rs` for the text replacement). This fix completes that unfinished Phase 2.
- **Files:** `[src/syncback/mod.rs](d:/UserGenerated/rojo/src/syncback/mod.rs)`, `[src/syncback/ref_properties.rs](d:/UserGenerated/rojo/src/syncback/ref_properties.rs)`, `[src/syncback/fs_snapshot.rs](d:/UserGenerated/rojo/src/syncback/fs_snapshot.rs)`
- **Problem:** `collect_referents(&new_tree, &pre_prune_paths, None)` is called at line 177 of `mod.rs` BEFORE the syncback walk that populates `ref_path_map`. The `None` means tentative paths (without dedup suffixes) are written into `Rojo_Ref_`* attributes. Then the post-hoc `fix_ref_paths` (lines 614-637) performs global text replacement across entire meta/model file contents to substitute tentative paths with final dedup'd paths. This is not attribute-scoped and can alter unrelated strings that happen to contain the same substring as a tentative path.
- **Existing infrastructure to build on:**
  1. `collect_referents` already accepts `final_paths: Option<&HashMap<Ref, String>>` (line 188 of `ref_properties.rs`).
  2. `ref_path_map` is already populated during the syncback walk with `(Ref, final_path)` entries.
  3. `tentative_fs_path_public` is already used at line 623 of `mod.rs` to compute tentative paths for the substitution diff.
- **Solution:** Move the `collect_referents` call from line 177 (before the syncback walk) to after the walk completes (after line 612). Pass `Some(&ref_path_map.borrow())` instead of `None`. Then remove or guard the `fix_ref_paths` block (lines 614-637) -- it should no longer be needed for any path that has a `final_paths` entry.
- **Ordering constraint:** `collect_referents` is currently called before property filtering (lines 179-198). Moving it after the syncback walk means it runs after filtering. Verify that `collect_referents` does not depend on properties that are removed by filtering (it should not -- it only reads Ref-type properties, which are not in the filtered set unless `ignore_referents` is true, in which case refs are skipped entirely).
- **Risk:** Medium; changes the ordering of the syncback pipeline. The infrastructure is already in place, reducing implementation risk.
- **Verify round-trip:** Scenario with duplicate-named ref target and non-ref string property containing same substring as tentative path; ensure only `Rojo_Ref_`* changes and non-ref string is untouched.
- **Verify syncback parity:** Compare CLI syncback and two-way outputs for refs targeting dedup-suffixed instances; paths must be byte-identical.
- **Tests required:**
  - Rust integration test in `[tests/tests/syncback_roundtrip.rs](d:/UserGenerated/rojo/tests/tests/syncback_roundtrip.rs)` validating non-ref string preservation while refs are rewritten correctly.
  - Rust integration test in `[tests/tests/two_way_sync.rs](d:/UserGenerated/rojo/tests/tests/two_way_sync.rs)` for dedup-aware ref persistence without text rewrite side effects.

### Fix 5: Add regression coverage for approved fixes

- **Status:** Approved
- **Finding:** Step 13 (missing coverage)
- **Files:** `[tests/tests/two_way_sync.rs](d:/UserGenerated/rojo/tests/tests/two_way_sync.rs)`, `[tests/tests/syncback_roundtrip.rs](d:/UserGenerated/rojo/tests/tests/syncback_roundtrip.rs)`, optionally helper fixtures under `[rojo-test/syncback-tests](d:/UserGenerated/rojo/rojo-test/syncback-tests)`.
- **Problem:** Current tests do not fully guard the four approved bug classes.
- **Solution:** Add targeted regression tests tied to Fixes 1-4 and ensure they fail pre-fix and pass post-fix.
- **Risk:** Low.
- **Verify round-trip:** Covered by added integration scenarios.
- **Verify syncback parity:** Add assertions comparing resulting file paths/attribute values against expected CLI-format output.
- **Tests required:**
  - All tests listed under Fixes 1-4.
  - One deterministic re-run assertion (second run no changes) for affected scenarios.

## Skipped Fixes

### Skipped: ProjectNode duplicate-child handling rewrite

- **Finding:** Step 2d / Step 11k
- **Problem:** Duplicate-named children under ProjectNode are currently skipped with warnings (`[src/snapshot_middleware/project.rs](d:/UserGenerated/rojo/src/snapshot_middleware/project.rs)` around `~587-683`).
- **Reason skipped:** User accepted as release limitation for now.

### Skipped: Globally optimal matcher replacement

- **Finding:** Step 11h (determinism/assignment quality)
- **Problem:** Greedy assignment may produce suboptimal pairing in rare ambiguous groups.
- **Reason skipped:** User accepted greedy behavior for this release.

## Accepted Limitations

- **Limitation:** ProjectNode duplicate-named children are skipped during syncback.
- **Scenario:** Under project-backed nodes, duplicate names are detected and omitted from child maps; warning logged.
- **User decision:** Accepted for this release.
- **Mitigation:** Keep explicit warning logs; add failing acceptance test (below) to track until fixed.
- **Limitation:** Greedy matching is not globally optimal.
- **Scenario:** Ambiguous duplicate groups can choose a local minimum causing rename churn.
- **User decision:** Accepted for this release.
- **Mitigation:** Add stress/failing test for known counterexample and keep deterministic tie behavior.

## Deferred Refactors

- Consolidate filesystem-segment derivation into one shared helper used by `[src/rojo_ref.rs](d:/UserGenerated/rojo/src/rojo_ref.rs)`, `[src/snapshot/tree.rs](d:/UserGenerated/rojo/src/snapshot/tree.rs)`, and `[src/web/api.rs](d:/UserGenerated/rojo/src/web/api.rs)` to eliminate duplicate naming logic. *(Continuing from `ambiguous_paths_audit_fixes_9d3ed6da` Deferred Refactors -- still open.)*
- Revisit optimal assignment algorithm for large ambiguous groups (major rewrite; out of current scope). *(Continuing from `ambiguous_paths_audit_fixes_9d3ed6da` Deferred Refactors -- still open.)*
- Phase 2e matching cache from the original plan (`ambiguous_path_handling_f2eaef11`): add optional cache mapping `parent_ref -> (children_list_hash, match_assignments)` to avoid re-running the full algorithm when children haven't changed. Optimization only, not needed for correctness. *(Never completed or cancelled across any subsequent plan -- explicitly deferred here.)*

## Test Plan

### Rust Unit Tests (`#[cfg(test)]`)

- Dedup cleanup metadata update helper behavior after rename (Fix 1).
- Added-path segment generation helper returns correct extension/suffix across middleware types (Fix 3).

### Rust Integration Tests (`tests/tests/`)

- Delete base dedup name then update promoted sibling in same serve session; verify writes hit new path and persist after rebuild (Fix 1).
- Batch-remove 2 of 3 same-named siblings; verify sole survivor is renamed from `Foo~2` to `Foo` (Fix 2).
- Batch-remove all members of a dedup group; verify no spurious rename attempts (Fix 2).
- Same `/api/write` request: add target + set Ref to target, verify persisted path includes expected extension/suffix (Fix 3).
- Ref rewrite safety: non-ref string fields are unchanged while `Rojo_Ref_`* gets final dedup path (Fix 4).

### Lua Spec Tests (`.spec.lua`)

- No mandatory Lua-side changes for approved fixes; optional guard test for same-batch add+ref behavior if plugin-side helper touched.

### Snapshot Tests (`insta`)

- Add or update syncback snapshot fixture showing final dedup-aware `Rojo_Ref_`* output without incidental string changes (Fix 4).

### Failing Tests for Known Limitations

- ProjectNode duplicate-named child round-trip identity test asserting correct behavior (expected to fail until limitation removed).
- Ambiguous-group matching counterexample test asserting globally optimal pairing (expected to fail with greedy algorithm).

## Test Rules

### For bugs found and fixed

- Each approved bug fix must have a regression test that fails pre-fix and passes post-fix.

### For missing coverage identified

- Add coverage in affected layer(s); investigate any unexpected failure as a potential additional bug.

### For known limitations (Accepted Limitations section)

- Write correctness-asserting tests even if they fail now.
- Leave them failing (do not ignore), to serve as future acceptance criteria.

### Scope

- Cover both persistence correctness (filesystem outputs) and in-memory tree consistency where applicable.

## Final Step: Run CI

After implementing all approved fixes and tests, run `/ci` and require a clean pass before considering this plan complete.