fix(dynamic-truncator): use provider-aware context limits

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/dynamic-truncator.test.ts

@@ -24,7 +24,10 @@ function resetContextLimitEnv(): void {
   }
 }
 
-function createContextUsageMockContext(inputTokens: number) {
+function createContextUsageMockContext(
+  inputTokens: number,
+  options?: { providerID?: string; modelID?: string; cacheRead?: number }
+) {
   return {
     client: {
       session: {
@@ -33,11 +36,13 @@ function createContextUsageMockContext(inputTokens: number) {
             {
               info: {
                 role: "assistant",
+                providerID: options?.providerID ?? "anthropic",
+                modelID: options?.modelID,
                 tokens: {
                   input: inputTokens,
                   output: 0,
                   reasoning: 0,
-                  cache: { read: 0, write: 0 },
+                  cache: { read: options?.cacheRead ?? 0, write: 0 },
                 },
               },
             },
@@ -99,4 +104,24 @@ describe("getContextWindowUsage", () => {
     expect(usage?.usagePercentage).toBe(0.3)
     expect(usage?.remainingTokens).toBe(700000)
   })
+
+  it("uses model-specific limit for non-anthropic providers when cached", async () => {
+    // given
+    const modelContextLimitsCache = new Map<string, number>()
+    modelContextLimitsCache.set("opencode/kimi-k2.5-free", 262144)
+    const ctx = createContextUsageMockContext(180000, {
+      providerID: "opencode",
+      modelID: "kimi-k2.5-free",
+    })
+
+    // when
+    const usage = await getContextWindowUsage(ctx as never, "ses_model_limit", {
+      anthropicContext1MEnabled: false,
+      modelContextLimitsCache,
+    })
+
+    // then
+    expect(usage?.usagePercentage).toBeCloseTo(180000 / 262144)
+    expect(usage?.remainingTokens).toBe(82144)
+  })
 })