Read session debt from Advance instead of duplicating scan (O4)

[JRedeker]

Summary

OCA currently has internal/advruntime/session_debt.go (388 LOC) that duplicates Advance's session-debt scan (plugin/src/utils/opencode-session-debt.ts, 237 LOC). Under the cleaner ownership boundary (Advance must work standalone; OCA enhances), Advance owns the scan logic and OCA reads the signal.

Why

• Advance needs session-debt detection for its own diagnostics (adv_status, agent context)
• OCA needs the signal for surfacing in oca doctor and oca adv-status, not its own scan
• Threshold logic should live once

Acceptance Criteria

• OCA deletes internal/advruntime/session_debt.go
• OCA reads session-debt signal via Advance's stable read surface (depends on ADV adding adv status --format json per O2)
• Threshold values live only in Advance
• oca doctor and oca adv-status continue to surface session-debt info correctly

Dependencies

Blocked by Advance adding stable read surface (new ADV issue tracked in cross-repo boundary audit § O2).

Proposal

docs/proposals/2026-05-08-cross-repo-boundary-audit.md § O4

WSJF Estimate

Value: 5 | TC: 3 | RROE: 5 | Effort: 2 | WSJF: 4.0

[JRedeker]

Remains blocked by OCA #24 (O2: Replace adv_status.sh with oca adv-status Go subcommand). OCA #24 requires Advance to expose adv status --format json first — that ADV issue has not been created yet.

This is the only remaining tech-debt item. Recommend creating the ADV companion issue and tackling OCA #24 before revisiting #25.

[JRedeker]

Companion issue created: Sharper-Flow/Advance#104 — adv status --format json stable read surface.

Dependency chain: ADV #104 → OCA #24 (oca adv-status Go subcommand) → OCA #25 (delete session_debt.go)