fix: storyboard floor drift — v6 sync_event_sources/log_event + negative-path markers + asap-timing IO gate

[bokelley]

Summary

Main was running at the exact 69-clean floor for /sales with 4 storyboards real-failing — any flake on media_buy_seller/audience_buy_flow's phantom-rejection step dropped it below floor. Three independent fixes:

• v6 TrainingSalesPlatform was missing syncEventSources + logEvent. SDK framework only advertises platform methods that exist, so sync_event_sources / log_event steps in event_dedup_flow and performance_buy_flow were silently skipped — leaving downstream create_media_buy steps rejected as "not registered." Wired both through to the v5 handlers with brand_domain threaded from ctx.account.ctx_metadata (same pattern as existing syncAudiences).
• expect_error: true missing on phantom-rejection steps in audience_buy_flow and performance_buy_flow. Both submit a create_media_buy with an intentionally-unregistered id and assert the rejection's error.field; the SDK runner needs the marker to invert pass/fail. Added expect_error: true + negative_path: payload_well_formed, mirroring invalid_transitions.
• proposal_finalize_asap_timing rejected with IO_REQUIRED. Scenario claimed io_acceptance was "intentionally omitted because requires_signature is false on this proposal" — but the training agent's seeded proposal carries requires_signature: true. Added context_outputs for io_id extraction and included io_acceptance on the asap create step. Discriminating assertion is the asap start_time form, not the IO gate.

After fixes, /sales lifts from 69→73 clean (350 passing). Floors bumped with +1 clean buffer:

Tenant	Old	New	Observed
signals	70:111	74:111	75
sales	69:315	72:340	73
governance	69:151	73:151	74
creative	69:169	73:169	74
creative-builder	66:146	70:146	71
brand	69:96	73:96	74

Reviewed by code-reviewer (safe to merge, no blockers) and ad-tech-protocol-expert (spec-conformant, preserves grading intent).

Known-failing follow-ups (not in this PR)

• dependency_impairment + dependency_impairment_cardinality (feat: 3.1.0 follow-ups — impairment_propagation, swap recovery, cardinality #4685/docs+compliance: terminal-buy carve-out (#4635) + dependency-impairment storyboard (#2860) #4677): need full impairment tracking in TA — creative-status transitions don't propagate to media_buy.impairments[], swap-assignment doesn't clear stale entries. Feature work.
• signed_requests-strict-required / strict-forbidden: SDK grader's covers_content_digest: 'either' permissiveness rule doesn't account for vectors that are structurally incompatible with a required-mode (or forbidden-mode) verifier. SDK-side fix or expanded skipVectors list.

Test plan

• bash scripts/run-storyboards-matrix.sh — all 6 tenants pass new floors
• tsc --noEmit -p server/tsconfig.json clean
• Pre-commit (unit tests + typecheck) green at push time
• Pre-push storyboard matrix green at push time

🤖 Generated with Claude Code