Fix opencode control agent model/variant propagation

[proboscis]

Summary

• propagate resolved control model/variant into opencode control-session creation flow
• persist opencode control-session metadata (port, model, model_variant) in .orch/control-session.json
• enforce model/variant-aware reuse for control sessions; if stored metadata mismatches, create a fresh control session
• add daemon tests proving resolved control model/variant reach SendMessagePrompt and metadata is persisted/reused correctly

Acceptance Criteria Evidence

1) Control agent uses opencode.default_model and default_variant from config

Verified by new test:

• go test ./internal/daemon -run 'TestResolvedControlModelAndVariantReachOpenCodeInitialPrompt' -count=1
• Result: ok github.com/s22625/orch/internal/daemon

This test writes project config with:

opencode:
  default_model: openai/gpt-5.3-codex
  default_variant: xhigh

Then verifies the resolved values are sent in initial /message payload.

2) Initial prompt to new control session includes configured model/variant

Verified by new/updated tests:

• go test ./internal/daemon -run 'TestGetOrCreateOpenCodeControlSessionCreatesWhenRecoveryFindsNoSession' -count=1
• Result: ok github.com/s22625/orch/internal/daemon

The test captures /session/{id}/message request and asserts model=openai/gpt-5.3-codex, variant=xhigh.

3) Reused control sessions also respect configured model/variant

Verified by tests:

• TestGetOrCreateOpenCodeControlSessionReusesExisting
• TestGetOrCreateOpenCodeControlSessionCreatesNewWhenStoredModelMismatches

Command:

• go test ./internal/daemon -run 'TestGetOrCreateOpenCodeControlSessionReusesExisting|TestGetOrCreateOpenCodeControlSessionCreatesNewWhenStoredModelMismatches' -count=1
• Result: ok github.com/s22625/orch/internal/daemon

Behavior now:

• stored control-session metadata includes model + model_variant
• reuse only occurs when stored model metadata matches current resolved config
• mismatch triggers fresh control-session creation with the configured model/variant

4) orch run continues to correctly pass model/variant (no regression)

Regression checks run:

• go test ./internal/daemon -run 'TestProtoStartRunFieldMapping|TestProtoContinueRunFieldMapping' -count=1
• go test ./internal/agent -run 'TestSendMessagePromptWithDirectoryAndModel' -count=1
• go test ./internal/daemon -count=1
• go build ./...

All passed.

5) Added test verifying ResolveControlModelAndVariant values reach SendMessagePrompt

Added:

• TestResolvedControlModelAndVariantReachOpenCodeInitialPrompt

It explicitly resolves values via ResolveControlModelAndVariant("opencode") and verifies those values are sent in the initial SendMessagePrompt payload.

Additional validation

• make lint passed (semgrep architecture lint)

Issue

• fixes orch-441