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The Read tool output format is being updated from spaces + line number + arrow to a more compact line number + tab format. The Edit tool description dynamically adapts to tell the model which format is in use, reducing confusion when matching indentation.
Evidence
Dynamic format description (search for "line number + tab") — controlled by tengu_compact_line_prefix_killswitch
[Gradual Rollout] — gated by tengu_compact_line_prefix_killswitch feature flag.
Strings lifted out of the shipped bundle, so the claim above can be checked against them.