feat(gsd): implement ADR-005 multi-model provider and tool strategy
Implements all 4 phases of ADR-005 (issue #2790):
Phase 1: Provider Capabilities Registry
- Declarative ProviderCapabilities interface and PROVIDER_CAPABILITIES
registry covering all 12 API providers
- Consolidates scattered *-shared.ts knowledge into queryable registry
- Unknown providers get permissive defaults (backward compatible)
Phase 2: Tool Compatibility Metadata
- ToolCompatibility interface (producesImages, schemaFeatures, minCapabilityTier)
- compatibility field on ToolDefinition
- Tool compatibility registry with pre-populated built-in tools
- Auto-registration from registerTool() and MCP tool defaults
Phase 3: Tool-Compat Filter + ProviderSwitchReport
- ProviderSwitchReport tracks thinking blocks dropped/downgraded,
tool call IDs remapped, synthetic results inserted, thought
signatures dropped during cross-provider message transformation
- isToolCompatibleWithProvider(), filterToolsForProvider(), adjustToolSet()
functions in model router
- filteredTools field on RoutingDecision
- Verbose output for filtered tools in auto-model-selection
Phase 4: adjustToolSet Extension Hook
- AdjustToolSetEvent and AdjustToolSetResult interfaces
- emitAdjustToolSet() on ExtensionAPI and ExtensionRuntime
- Default no-op handler in register-hooks.ts
Includes 47 new tests (20 provider caps + 10 switch report + 17 tool compat)
Closes #2790
b1c0dafc70