feat: make default workflow domain configurable at runtime

[mrsimpson]

Summary

Eliminate hardcoded 'code' default domain in WorkflowManager and provide runtime domain switching for long-lived processes (MCP server, OpenCode plugin).

Changes

• Four-level env var chain: constructor param > WORKFLOW_DOMAINS > DEFAULT_DOMAINS > VIBE_WORKFLOW_DOMAINS > empty Set (all workflows)
• defaultDomains constructor parameter for programmatic override (library consumers, testing)
• DEFAULT_ALL_DOMAINS env var for getAllAvailableWorkflows() — replaces incomplete hardcoded list
• setDomains() method for runtime domain switching with validation against known domains
• DOMAIN_DESCRIPTIONS constant with meaningful summaries of what each domain is suitable for
• load_workflows tool — simple enum parameter, domain descriptions exposed via domain:// resource
• domain:// resource — exposes all available domains with descriptions for LLM discovery
• Bug fix: loadPredefinedWorkflows() now clears maps before reloading (prevents workflow accumulation)

Tests

• 18 new tests: 9 for env var precedence chain, 9 for setDomains()
• All existing tests pass (except 1 pre-existing unrelated failure in game-beginner.yaml)

Architecture Decision

Domain descriptions are exposed as a resource (domain://) rather than embedded in the tool parameter. This keeps the tool schema lean and reduces LLM context usage. The LLM can query the resource to discover domains before calling load_workflows.

Affected Files

• packages/core/src/workflow-manager.ts — core changes
• packages/core/test/unit/workflow-domains-precedence.test.ts — 9 new tests
• packages/core/test/unit/workflow-domain-switching.test.ts — 9 new tests (new file)
• packages/core/test/unit/workflow-domain-filtering.test.ts — updated for empty Set default
• packages/mcp-server/src/server-config.ts — register load_workflows tool + domain:// resource
• packages/mcp-server/src/tool-handlers/load-workflows.ts — simplified handler (new file)
• packages/mcp-server/src/tool-handlers/index.ts — register handler
• packages/opencode-plugin/src/plugin.ts — register load_workflows tool
• packages/opencode-plugin/src/tool-handlers/load-workflows.ts — simplified handler (new file)

Backward Compatibility

• VIBE_WORKFLOW_DOMAINS still works as lowest-priority env var
• Adding options?: WorkflowManagerOptions to constructor is backward compatible
• Empty Set fallback loads ALL workflows (superset of old code default)

UX: No Active Workflow Prompt

When no workflow is active, the plugin injects this message (unchanged):

No Active Workflow Detected. You MUST initiate a new development workflow before proceeding. First, create a new branch with a meaningful name using a conventional commit prefix (e.g., feat/add-new-feature, fix/bug-description, refactor/improve-logic). Then call the start_development tool to begin. Do NOT attempt any file edits or tool executions until a workflow is active.

[mrsimpson]

@claude Review once