fix: forward on insert.text breaks undo batching

[christianhg]

Problem

When a behavior uses forward(event) on insert.text with a second action set, each typed character becomes its own undo step instead of merging with adjacent characters.

This breaks the expected undo behavior for any behavior that observes text insertion without modifying it (e.g., a behavior that forwards the text and then checks the block content to update styles).

Root cause

performEvent sets a unique undoStepId for every insert.text event because it's synthetic (not in nativeBehaviorEventTypes). Without custom behaviors, the default handler clears undoStepId before running the operation, so consecutive characters merge. But when a behavior forwards the event, defaultBehaviorOverwritten = true and the clearing never happens. Each character gets a unique undoStepId, preventing history merge.

Status

Failing tests added. Fix pending.

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Project	Deployment	Actions	Updated (UTC)
portable-text-editor-documentation	Ready	Preview, Comment	Feb 23, 2026 5:55pm
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portable-text-playground	Ready	Preview, Comment	Feb 23, 2026 5:55pm

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