test(orchestration): cover bounded V2 socket fallback paging

[saphid]

Bounded socket fallbacks must preserve history cursors so clients can fetch earlier items after HTTP failure or reconnect. Julius implemented the production behavior in V2 commit 79634b140; this PR now adds regression coverage against that implementation.

Keep the current transport redaction, row budgets and legacy-client capability negotiation intact. Cover bounded snapshot metadata, schema decoding, replacing a stale cached cursor, and loading an earlier page after HTTP seeding fails.

Current head 589f12390 is rebuilt on V2 7dd9873ed with test-only prerequisite #10865 (merge first). Topic delta is four test files; no production behavior changes remain.

Validation: 95 focused server/contracts/client-runtime tests pass; all three package typechecks, targeted lint and formatting pass. New CI pending. Independent Claude Opus 5 high review unavailable: direct launcher exited 1 on expired OAuth before inference.

Targets V2 #2829. Updated with GPT-6 in Codex/T3.

[macroscopeapp]

Approvability

Verdict: Approved at 589f123

Macroscope's review found this PR approvable — This PR updates only server, client-runtime, and contract tests, adding regression coverage for existing bounded socket fallback and history paging behavior. It does not modify production implementation, schemas, defaults, deployment, or static-analysis configuration.

Notes:

• No code objects were reviewed. Approvability was decided on eligibility alone.

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[saphid]

Ran an independent automated first-pass review (Amp/Astra) over the 8-file diff against 415ed0f.

• 1 finding: bounded socket snapshots could silently degrade older V2 clients (no capability negotiation). Dismissed as false positive at high severity: the new fields are optionalKey and excess keys are dropped on decode, so legacy clients don't break; V2 is unreleased (targets feat(orchestrator): introduce new orchestrator #2829) so no shipped old-client population, and mixed nightlies already surface a version-mismatch warning. Residual: mixed-version fallback shows only the window with no load-earlier until versions sync. A negotiation/bump feels disproportionate for an unreleased branch.
• No other findings; no code changes pushed.