Why: F02/F04/F15 - contract requests shared one transcript across
session scopes, Writable was dropped, and a torn JSONL tail poisoned
the next append; pure-text contract results lost their text.
Evidence: adapters/native, runtime/session, runtime/tools and
conformance tests pass (verify-u2.json); scope-isolation, write-set and
torn-tail regression cases added.
Impact: empty scope keeps legacy one-shot semantics; identity-less old
transcripts are never auto-adopted by a new scope.
Refs: feature/agent-stack-audit-remediation-b1 U2
Why: Linear transcripts cannot fork, and compaction rewrote history, so resume and branch navigation had nothing to point at.
Evidence: go test -count=1 ./runtime/session/
Impact: Load still returns the model-visible path, including old one-message-per-line files. Compaction appends a summary entry instead of truncating the file.
Refs: feature/pi-headless N1
Co-authored-by: Cursor <cursoragent@cursor.com>
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