fix(anthropic-context-window-limit-recovery): remove emergency fallback message revert logic

Remove the FallbackState interface and related fallback recovery mechanism that deleted message pairs when all other compaction attempts failed. This simplifies the recovery strategy by eliminating the last-resort fallback approach.

Changes:
- Removed FallbackState interface and FALLBACK_CONFIG from types.ts
- Removed fallbackStateBySession from AutoCompactState
- Removed getOrCreateFallbackState and getLastMessagePair functions
- Removed emergency revert block that deleted user+assistant message pairs
- Updated clearSessionState and timeout reset logic
- Removed related test cases

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/hooks/anthropic-context-window-limit-recovery/executor.test.ts

@@ -15,7 +15,6 @@ describe("executeCompact lock management", () => {
       pendingCompact: new Set<string>(),
       errorDataBySession: new Map(),
       retryStateBySession: new Map(),
-      fallbackStateBySession: new Map(),
       truncateStateBySession: new Map(),
       dcpStateBySession: new Map(),
       emptyContentAttemptBySession: new Map(),
@@ -68,38 +67,6 @@ describe("executeCompact lock management", () => {
     expect(autoCompactState.compactionInProgress.has(sessionID)).toBe(false)
   })
 
-  test("clears lock when revert throws exception", async () => {
-    // #given: Force revert path by exhausting retry attempts and making revert fail
-    mockClient.session.revert = mock(() =>
-      Promise.reject(new Error("Revert failed")),
-    )
-    mockClient.session.messages = mock(() =>
-      Promise.resolve({
-        data: [
-          { info: { id: "msg1", role: "user" } },
-          { info: { id: "msg2", role: "assistant" } },
-        ],
-      }),
-    )
-
-    // Exhaust retry attempts
-    autoCompactState.retryStateBySession.set(sessionID, {
-      attempt: 5,
-      lastAttemptTime: Date.now(),
-    })
-    autoCompactState.errorDataBySession.set(sessionID, {
-      errorType: "token_limit",
-      currentTokens: 100000,
-      maxTokens: 200000,
-    })
-
-    // #when: Execute compaction
-    await executeCompact(sessionID, msg, autoCompactState, mockClient, directory)
-
-    // #then: Lock cleared even though revert failed
-    expect(autoCompactState.compactionInProgress.has(sessionID)).toBe(false)
-  })
-
   test("shows toast when lock already held", async () => {
     // #given: Lock already held
     autoCompactState.compactionInProgress.add(sessionID)
@@ -195,9 +162,6 @@ describe("executeCompact lock management", () => {
       attempt: 5,
       lastAttemptTime: Date.now(),
     })
-    autoCompactState.fallbackStateBySession.set(sessionID, {
-      revertAttempt: 5,
-    })
     autoCompactState.truncateStateBySession.set(sessionID, {
       truncateAttempt: 5,
     })