* perf(session-load): memoize the compression-lineage display stitch
_webui_sidecar_lineage_messages_for_display re-merged multi-thousand-row
parent+child transcripts on EVERY GET /api/session (measured 5.1s per
request on a real 5.2k-message lineage, py-spy: merge_session_messages_
append_only + _matching_visible_duplicate dominate). The merge result is
now cached per session id, validity keyed by the exact stat signature of
the child sidecar AND every snapshot parent involved, bounded LRU(16).
Any write to any involved sidecar invalidates naturally; cache hits and
the populating call hand out shallow-copied rows so caller-side display
metadata cannot corrupt cached state.
Measured: 5.17s cold -> 0.002s warm on the real session; invalidation
after touch re-merges. Tests: tests/test_lineage_display_cache.py
(correctness, copy isolation, child/parent invalidation, no pollution
for lineage-less sessions).
* perf(api): memoize inactive-session display merges
* perf(api): skip state load on cached transcript reopen
* test(api): remove unused lineage-cache import
* fix(api): reject streaming key without state database
* test(api): isolate display cache fixture
* fix(api): bind cache publication to read signature
* fix(api): harden display cache invalidation
* fix(api): bind cache hits to lineage provenance
* fix(api): close remaining display cache scope races
* fix(api): scope display cache revision to target
* fix(api): evict unverifiable lineage provenance
* fix(api): keep incomplete lineage provenance uncached
---------
Co-authored-by: Anthony Ruiz <ruizanthony@users.noreply.github.com>
