Add durable verified workers and broader model access

[inquerium]

What this changes

Delegated coding work can now be submitted as durable jobs with isolated Git snapshots, bounded repair, explicit outcomes, and verified patch application. Jobs survive client disconnects and share provider capacity. The model browser and engine adapter expose connected providers while preserving free-only defaults and requiring explicit paid-model selection.

The change also fixes delegation failures being presented as success, preserves retrievable tool output and long-task constraints, and adds optional scoped engine workers plus detailed cache/request accounting. Standard engine behavior remains the default.

These runtime changes share the same execution and model-policy contracts, so they are delivered as one integrated foundation. Follow-up request tracing and verification-aware completion will be reviewed separately.

How it was tested

• All 15 deterministic regression suites pass (npm run test:regression), including MCP/daemon multi-client recovery, ownership, repair accounting, and interrupted benchmark recovery.
• npm run test:boot passed on local macOS arm64; gateway model discovery returned HTTP 200.
• Syntax checks and git diff --cached --check pass.
• Completed 12 live free-model coding jobs: scoped accepted 4/6 versus standard 3/6 and used 31.6% less total observed input. Five unaccepted jobs remain in the accounting. This is a six-task controlled-regression experiment, not a general coding ranking.
• Reproducible benchmark harness, sanitized results, and patches: benchmarks/results/2026-09-20/.

Notes for reviewers

No new runtime dependencies. CI/release workflows now require deterministic regressions. Private session reviews and memory drafts are excluded. Worktrees are edit isolation, not process sandboxes; provider quotas still apply. No installer build or local Windows/Linux validation was performed. Nothing is merged or released by this PR.