Merge a2acc7d3eb620bb52f09f7ea3b5a3a1c23353e18 after preserving the earlier
master checkpoint and its successful CI. Carry current provider input-history
handling, UI controls, agent targeting, and runner-concurrency changes into
the integration base without changing the Session migration feature layers.
Keep durable direct-child catalog semantics alongside the upstream running /
inactive vocabulary. Resolve the snapshot description conflicts by retaining
that upstream status text and the existing descendants-only diagnostic rule;
the source and all 53 JSON tool descriptions agree. Preserve parent-session
availability handling with the upstream stale-blank and batched-history fixes.
The merged application builds, all 41 documentation gates pass, and focused
provider, tool-control, and Session Controller tests pass (98, 29, and 125).
Recorded input changes come from master: one refreshed v3 list-agents sample
and three new v3 scenarios; no migration bumps an existing snapshot generation.
Regenerate only native V3 Session/output oracles through the shipped headless and SDK profiles. These outputs retain system-message admission before users, bind request metadata before title fallback, and record real V3 delivery acknowledgments. Historical V0/V1/V2 replay inputs remain unchanged; pinned scenarios keep separate writer outputs.
The upper headless/SDK refresh covered109 cases; the only initial failure used macOS system Python3.9 for the PTC Python scenario, which passed with the declared CPython3.14 PATH. No assertion or runtime behavior was changed to accommodate it.
Restore all 147 historical canonical fixtures changed by the lower branch to exact shared base 220ff708e3628a9be46d9747d09af6d8cd742f0d bytes (145 V2 and two V0). All 180 committed V0/V1/V2 canonical files now have zero diff against that base, including unchanged Python, test-support and preview sources.
Preserve corrected lower writer bodies in 146 V3 successors across 119 owner directories: replace 135 unreleased V3 counterparts and add 11 siblings. Change only each copied Session header version; preserve all body bytes, raw model streams, inline images, IDs, references and historical delivery generation markers. Remove two unshipped V2 additions after creating their V3 sibling: record-suite/rec-pin and empty-response-retry-current.
Keep six explicitly historical snapshot owners pinned with no V3 sibling. Restore the two pre-step V0 record child sources without synthesizing current output. Fix seven embedded Session header versions in exactly five test-support behavior owners whose output filenames already select V3. Leave protocol expectations, shared references, sidecars, consumer scripts and production migration/normalization code untouched.
Validation: purpose-built temporary Python inventory and verifier checked 337 canonical headers, 3714 successor JSON rows, message roles, contiguous child roles, exact successor bodies, all 180 historical base bytes and zero git diff, noncanonical JSONL immutability, six retained owners and six unchanged preview fixtures. git diff --cached --check passed. Temporary generators removed. Strict migration, native refresh and replay remain pending parent integration; unsupported pre-step sources are reported separately.
Consolidate the representation-change PR and its rebase reconciliations into one baseline. Preserve the exact tree and keep the in-history feature in the dependent PR. Follow-up fixes remain separate.
Tianyi Cui