feat(sleep): add OpenCode integration and backend

[norandom]

Summary

• add an OpenCode integration with /sleep command, skill, installer, and MCP wiring
• mine native OpenCode sessions from ~/.local/share/opencode/opencode.db via read-only SQLite
• add --backend opencode using opencode run for model-backed replay, judging, mining, and reflection
• wire OpenCode path/model/source options through CLI, MCP, experiments, docs, and tests

Validation

• python3 -m py_compile skillopt_sleep/backend.py skillopt_sleep/main.py skillopt_sleep/cycle.py skillopt_sleep/experiments/run_experiment.py skillopt_sleep/experiments/run_gbrain.py skillopt_sleep/experiments/run_transfer.py skillopt_sleep/experiments/sweep.py plugins/copilot/mcp_server.py
• python3 -m pytest -q

Note: I did not run a live opencode model call to avoid spending user budget; subprocess behavior is covered with mocked tests.

[norandom]

@microsoft-github-policy-service agree [company="Because Security"]
@microsoft-github-policy-service agree company="Because Security"

[norandom]

@microsoft-github-policy-service agree

[Yif-Yang]

Review feedback

Thanks for the OpenCode integration — the SQLite session mining and --backend opencode support are useful additions.

However, this PR cannot be merged as-is because it removes existing features that are actively used on main:

Removed	Impact
ThreadPoolExecutor parallelism in replay_batch() / multi_rollout()	All replay becomes serial — significantly slower for real API backends
scheduler.py (138 LoC) + schedule/unschedule CLI commands	Built-in cron scheduling removed
_task_guardrail() function	SpreadsheetBench output-contract safety check removed
TaskRecord.system field	Research benchmarks with custom rollout system prompts break
sample_id threading from attempt() / replay_one()	Cache-safe K-rollout removed
Gate-off path in consolidate.py	Now always runs val scoring even when gate is off (wasted API cost)

The PR is net −906 lines — most of those deletions are existing features, not dead code.

Requested action: Please rebase onto the latest main and keep only the additive changes:

• New OpenCodeBackend class + harvest_opencode.py (SQLite mining)
• --source opencode / --backend opencode CLI wiring
• Tests for the new backend
• Plugin files (plugins/opencode/)
• Doc updates

All existing backends, parallelism, scheduler, guardrails, and TaskRecord.system should be preserved as they are on main. The rebase conflicts are all in docs/scripts — the Python-side conflict in backend.py is just adding your new dispatch alongside the existing ones.