fix(shared): return GA 1M context limit for Anthropic 4.6/4.7 models without cached entry

Anthropic made the 1M context window GA for Opus 4.6, Sonnet 4.6, and 4.7 models on March 13, 2026 — no beta header required. The resolver was still falling back to 200K when no modelContextLimitsCache entry existed, causing premature compaction and over-truncation.

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

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

src/shared/context-limit-resolver.test.ts

@@ -158,6 +158,76 @@ describe("resolveActualContextLimit", () => {
     expect(actualLimit).toBe(200_000)
   })
 
+  it("returns GA 1M for claude-sonnet-4-6 without cached limit (GA context window)", () => {
+    // given
+    delete process.env[ANTHROPIC_CONTEXT_ENV_KEY]
+    delete process.env[VERTEX_CONTEXT_ENV_KEY]
+
+    // when
+    const actualLimit = resolveActualContextLimit("anthropic", "claude-sonnet-4-6", {
+      anthropicContext1MEnabled: false,
+    })
+
+    // then
+    expect(actualLimit).toBe(1_000_000)
+  })
+
+  it("returns GA 1M for claude-opus-4-6 without cached limit (GA context window)", () => {
+    // given
+    delete process.env[ANTHROPIC_CONTEXT_ENV_KEY]
+    delete process.env[VERTEX_CONTEXT_ENV_KEY]
+
+    // when
+    const actualLimit = resolveActualContextLimit("anthropic", "claude-opus-4-6", {
+      anthropicContext1MEnabled: false,
+    })
+
+    // then
+    expect(actualLimit).toBe(1_000_000)
+  })
+
+  it("returns GA 1M for claude-opus-4-7 without cached limit (GA context window)", () => {
+    // given
+    delete process.env[ANTHROPIC_CONTEXT_ENV_KEY]
+    delete process.env[VERTEX_CONTEXT_ENV_KEY]
+
+    // when
+    const actualLimit = resolveActualContextLimit("anthropic", "claude-opus-4-7", {
+      anthropicContext1MEnabled: false,
+    })
+
+    // then
+    expect(actualLimit).toBe(1_000_000)
+  })
+
+  it("returns GA 1M for claude-sonnet-4-6-high without cached limit (GA context window)", () => {
+    // given
+    delete process.env[ANTHROPIC_CONTEXT_ENV_KEY]
+    delete process.env[VERTEX_CONTEXT_ENV_KEY]
+
+    // when
+    const actualLimit = resolveActualContextLimit("anthropic", "claude-sonnet-4-6-high", {
+      anthropicContext1MEnabled: false,
+    })
+
+    // then
+    expect(actualLimit).toBe(1_000_000)
+  })
+
+  it("returns GA 1M for GA models on google-vertex-anthropic without cached limit", () => {
+    // given
+    delete process.env[ANTHROPIC_CONTEXT_ENV_KEY]
+    delete process.env[VERTEX_CONTEXT_ENV_KEY]
+
+    // when
+    const actualLimit = resolveActualContextLimit("google-vertex-anthropic", "claude-sonnet-4-6", {
+      anthropicContext1MEnabled: false,
+    })
+
+    // then
+    expect(actualLimit).toBe(1_000_000)
+  })
+
   it("returns null for non-Anthropic providers without a cached limit", () => {
     // given
     delete process.env[ANTHROPIC_CONTEXT_ENV_KEY]

src/shared/context-limit-resolver.ts

@@ -1,6 +1,7 @@
 import process from "node:process"
 
 const DEFAULT_ANTHROPIC_ACTUAL_LIMIT = 200_000
+const ANTHROPIC_GA_1M_LIMIT = 1_000_000
 export type ContextLimitModelCacheState = {
   anthropicContext1MEnabled: boolean
   modelContextLimitsCache?: Map<string, number>
@@ -15,11 +16,11 @@ function getAnthropicActualLimit(modelCacheState?: ContextLimitModelCacheState):
   return (modelCacheState?.anthropicContext1MEnabled ?? false) ||
     process.env.ANTHROPIC_1M_CONTEXT === "true" ||
     process.env.VERTEX_ANTHROPIC_1M_CONTEXT === "true"
-    ? 1_000_000
+    ? ANTHROPIC_GA_1M_LIMIT
     : DEFAULT_ANTHROPIC_ACTUAL_LIMIT
 }
 
-function supportsCachedAnthropicLimit(modelID: string): boolean {
+function hasGA1MContext(modelID: string): boolean {
   return /^claude-(opus|sonnet)-4(?:-|\.)(?:6|7)(?:-high)?$/.test(modelID)
 }
 
@@ -30,10 +31,12 @@ export function resolveActualContextLimit(
 ): number | null {
   if (isAnthropicProvider(providerID)) {
     const explicit1M = getAnthropicActualLimit(modelCacheState)
-    if (explicit1M === 1_000_000) return explicit1M
+    if (explicit1M === ANTHROPIC_GA_1M_LIMIT) return explicit1M
 
     const cachedLimit = modelCacheState?.modelContextLimitsCache?.get(`${providerID}/${modelID}`)
-    if (cachedLimit && supportsCachedAnthropicLimit(modelID)) return cachedLimit
+    if (cachedLimit && hasGA1MContext(modelID)) return cachedLimit
+
+    if (hasGA1MContext(modelID)) return ANTHROPIC_GA_1M_LIMIT
 
     return DEFAULT_ANTHROPIC_ACTUAL_LIMIT
   }