fix: use default power level when one isn't in state

[debdutdeb]

https://rocketchat.atlassian.net/browse/FDR-140

Summary by CodeRabbit

• Bug Fixes
  • Improved stability when processing room state by safely handling missing power settings, preventing rare crashes and sync failures in rooms with incomplete or corrupted history.
  • Reduces unexpected errors during membership changes, event authorization, and timeline loading in affected rooms.
  • Users should experience fewer sync interruptions, smoother room access, and more consistent behavior across clients when joining or viewing older rooms.

[coderabbitai]

Walkthrough

Introduces a null-safe fallback for missing power level events in resolveStateV2Plus by defaulting to a new PowerLevelEvent().toEventBase() when not found in partiallyResolvedState. Adds the corresponding import and removes an unused import. No other logic or public APIs are altered.

Changes

Cohort / File(s)	Summary of Changes
State resolution v2 power level fallback packages/room/src/state_resolution/definitions/algorithm/v2.ts	Added import for PowerLevelEvent; removed unused import. In resolveStateV2Plus, replaced non-null assertion of power level event with a nullish-coalescing fallback to new PowerLevelEvent().toEventBase(), changing control flow to always provide a default event base when missing.

Sequence Diagram(s)

sequenceDiagram
  autonumber
  participant R as resolveStateV2Plus
  participant S as partiallyResolvedState
  participant P as PowerLevelEvent

  R->>S: get("m.room.power_levels")
  alt Event exists
    S-->>R: powerLevelEventBase
    note right of R: Use retrieved event base
  else Missing
    R->>P: new PowerLevelEvent()
    P-->>R: toEventBase()
    note right of R: Use default event base
  end

  R->>R: Continue state resolution with event base

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

I nudge the state with gentle paws,
When power’s lost, I mind the laws—
A default seed I softly place,
So flows can hop at steady pace.
Thump-thump! No gaps, no fright—
The room now keeps its power right. 🐇✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title Check	✅ Passed	The title "fix: use default power level when one isn't in state" directly and concisely reflects the primary change in the diff: replacing a required power_level assertion with a fallback default PowerLevelEvent when the event is missing. It is specific to the behavioral fix, uses clear language, and is understandable by teammates scanning the commit history.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

✨ Finishing touches

• 📝 Generate Docstrings

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fdr140

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.01%. Comparing base (19bcb9b) to head (be2b806).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #206   +/-   ##
=======================================
  Coverage   81.01%   81.01%           
=======================================
  Files          63       63           
  Lines        4692     4692           
=======================================
  Hits         3801     3801           
  Misses        891      891           

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

packages/room/src/state_resolution/definitions/algorithm/v2.ts (1)

269-273: Good fallback; verify the synthetic PL event shape won’t break mainline ordering.

Defaulting to a PL event avoids crashes when it’s missing, but please confirm:

• PowerLevelEvent().toEventBase() returns a PersistentEventBase with type 'm.room.power_levels' and state_key ''.
• It includes required fields used by mainlineOrdering (e.g., eventId, origin_server_ts) or that mainlineOrdering does not depend on them for the PL pivot.
• Passing a non-persisted/synthetic event won’t trigger wrappedStore lookups by eventId.

If any of the above aren’t guaranteed, consider guarding mainlineOrdering to treat a “synthetic PL” as a pure config carrier (no lookups), or inject a sentinel eventId to avoid accidental fetches.

Also suggest adding a brief comment here to document why a default PL is safe per the Matrix spec defaults.

Add a focused test to lock this in:

// pseudo-test
it('resolves when no m.room.power_levels in partiallyResolvedState', async () => {
  // construct states with no PL event
  const result = await resolveStateV2Plus(statesWithoutPL, store);
  expect(result).toBeInstanceOf(Map);
  // optionally: assert deterministic ordering of a small conflicting set
});

📜 Review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 19bcb9b and be2b806.

📒 Files selected for processing (1)

• packages/room/src/state_resolution/definitions/algorithm/v2.ts (2 hunks)

🧰 Additional context used

🧬 Code graph analysis (1)

packages/room/src/state_resolution/definitions/algorithm/v2.ts (1)

packages/room/src/state_resolution/definitions/definitions.ts (1)

• getStateMapKey (10-15)

🔇 Additional comments (1)

packages/room/src/state_resolution/definitions/algorithm/v2.ts (1)

62-62: Import looks correct and scoped to usage.

Pathing aligns with existing manager imports. No issues.