feat: context window from model endpoints + percentage-based auto-compact

ModelInfo (kernel contract):
- Add contextWindow?: number field

OpenAI-stream listModels:
- Parse contextWindow from common field names (context_length,
  context_window, max_context_length, max_tokens)

Transport-contract:
- ModelsResponse: add optional modelInfo map (model name → { contextWindow? })
- Add ModelMetadata type
- Rename CompactThresholdResponse → CompactPercentResponse
- Rename SetCompactThresholdRequest → SetCompactPercentRequest

Credential store:
- Add getModelInfo(modelName) method — resolves full ModelInfo
  (including contextWindow) for a <credential>/<model> string

Transport-http:
- GET /models now includes modelInfo with contextWindow per model
- Rename compact-threshold endpoints → compact-percent

Session-orchestrator:
- Auto-compact now uses contextSize (not overcounted usage.inputTokens)
  compared against contextWindow * (percent / 100)
- Default percent: 85 (was flat 350000)
- resolveModelInfo dep added to look up contextWindow
- Passes modelName from the settled turn to the compaction service

Conversation store:
- Rename getCompactThreshold/setCompactThreshold → getCompactPercent/setCompactPercent
- compactThresholdKey → compact-percent key

1 files changed, 2 insertions, 0 deletions

diff --git a/packages/kernel/src/contracts/provider.ts b/packages/kernel/src/contracts/provider.ts
index 7f920c5..52d853b 100644
--- a/packages/kernel/src/contracts/provider.ts
+++ b/packages/kernel/src/contracts/provider.ts
@@ -112,6 +112,8 @@ export interface ProviderStreamOptions {
 export interface ModelInfo {
 	readonly id: string;
 	readonly displayName?: string;
+	/** The model's max context window in tokens (e.g. 200000). Optional — providers that don't report it leave it undefined. */
+	readonly contextWindow?: number;
 }
 
 /**