Review correctness of Jujutsu changes

Review the Jujutsu changes for the target revision, and report defects that make the code behave incorrectly or incompletely.

Follow the common review instructions: @../review-common.md

Main goals

Take the revision description and the surrounding code as the statement of intent, and find code that:

• does not do what it is meant to do: wrong logic, inverted condition, off by one, misused API
• breaks on states it should handle: edge case, empty or missing value, overflow, concurrent access
• silently ignores an error or abnormal condition instead of surfacing it
• is incomplete: unhandled case, code path left unimplemented, change applied in one place but not in its siblings
• reaches for a fragile or suboptimal pattern when a sound alternative exists: a polling loop with a sleep call where an event, condition variable or blocking wait would do
• carries algorithmic complexity that can explode at runtime on realistic inputs when a lower complexity alternative exists: a quadratic scan inside a loop where a set lookup or precomputed index would do

Guidelines

• Only report a defect if you can describe the concrete scenario that triggers it, and its consequence
• Do not report a bare suspicion: either exhibit the triggering input, or name what blocked you from confirming it
• Flag algorithmic complexity only when a realistic input can make its cost explode and a better alternative exists; small performance micro optimizations are out of scope
• Stay on correctness: readability, documentation and test coverage are covered by other review domains

Severity

Anchor severity to what the defect does when it triggers:

• critical — data loss, corruption, a crash, a hang or a security hole on a path ordinary use reaches
• major — a wrong result or a stall on a plausible input
• minor — a defect whose trigger is far-fetched or whose consequence the caller absorbs