Fix overlapping MutationObserver registrations, with credit to #68

[byteface]

When one MutationObserver watches a child directly and its ancestor with subtree and old-value capture enabled, the direct registration previously hid the ancestor's old-value request. Combine all matching registrations and deliver one record with the requested old value for attributes and character data.

Adapted from 7HR4IZ3's interestedObservers aggregation in #68, with credit in the code and tests and a verified Co-authored-by trailer.

Also reject contradictory observe options, infer omitted mutation types from option presence, and release inactive observers from the global registry. Synchronous delivery is documented; browser microtask batching remains unimplemented.

Validation: 248 tests and 89 subtests passed across tests/test_dom_mutation_observer.py, tests/test_dom.py, and tests/test_dom_insertion_ownership.py. The 22 new cases produce 11 failures against the unchanged baseline and all pass after the fix. The principal regression is test_overlapping_observations_preserve_old_value, covering attributes and character data, both registration orders, and old-value requests on either registration.

Follow-up to #68.

[qodo-code-review]

PR Summary by Qodo

Preserve old values across overlapping MutationObserver registrations

🐞 Bug fix 🧪 Tests 🕐 20-40 Minutes

AI Description

• Aggregate overlapping observer registrations into one record while preserving requested old
 values.
• Normalize and validate observation options, and release disconnected observers from global
 tracking.
• Add mutation regressions and make Git tests independent of checkout branch state.

Diagram

graph TD
  A["DOM Mutation"] --> B["Observer Registry"] --> C{"Matching registration?"}
  C -->|Yes| D["Aggregate options"] --> E["Single record"] --> F["Sync callback"]
  C -->|No| G["Ignore mutation"]

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High-Level Assessment

The PR uses the appropriate registration-aggregation strategy: evaluate every eligible direct and ancestor registration, combine old-value requirements, and emit one observer-level record. First-match delivery would retain the original ordering bug, while emitting per-registration records would introduce duplicates. Explicit removal from the strong global registry also preserves active delivery while allowing disconnected observers to be collected; a weak-only registry could prematurely lose active observers.

Files changed (3) +212 / -35

Bug fix (1) +49 / -33

dom.pyCorrect MutationObserver aggregation, validation, and lifecycle behavior +49/-33

Correct MutationObserver aggregation, validation, and lifecycle behavior

• Combines all matching direct and ancestor registrations before creating one MutationRecord, preserving an old value requested by any eligible registration without duplicate delivery. It also infers mutation types from present dependent options, rejects contradictory options, tracks only active observers globally, and documents synchronous callback delivery.

domonic/dom.py

Tests (2) +163 / -2

test_dom_mutation_observer.pyAdd comprehensive MutationObserver regression coverage +141/-0

Add comprehensive MutationObserver regression coverage

• Adds parameterized tests for overlapping registrations, registration ordering, old-value aggregation, subtree and filter exclusions, option inference and validation, disconnect reuse, and garbage collection. The tests credit the interested-observer approach adapted from PR #68.

tests/test_dom_mutation_observer.py

test_terminal.pyMake Git terminal tests safe for detached HEAD checkouts +22/-2

Make Git terminal tests safe for detached HEAD checkouts

• Replaces the assumption that the project checkout uses the master branch with an isolated temporary Git repository. The test now verifies clean and untracked status output in both attached and detached HEAD states.

tests/test_terminal.py

[qodo-code-review]

Code Review by Qodo

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