dcdpr / jp / 26630395827

66%

push

github

perf(conversation): Fix O(n²) clone cost in `Extend` impl (#689)

The `Extend<ConversationEventWithConfig>` impl previously delegated to
`push_with_config_delta` on every iteration. That method called
`self.last()` each time, which walks the entire event stream and
deep-clones `PartialAppConfig` to compute the tail config. For a stream
with n events this meant n full walks — O(n²) in clones.

The fix inlines the delta logic directly into the `extend` loop and
caches a running `tail` config across iterations. Each step now clones
only the current config value, reducing the cost to O(n). The removed
`push_with_config_delta` helper is no longer needed.

A characterization test is added to guard the impl: it verifies that
extending an empty stream from a source stream reproduces both the
observed iter sequence and the serialized on-disk shape of the source.

This performance problem was found using the new `jp_debug` tool-suite.

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Signed-off-by: Jean Mertz <git@jeanmertz.com>

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