diff --git a/src/hooks/compaction-context-injector/constants.ts b/src/hooks/compaction-context-injector/constants.ts
new file mode 100644
index 000000000..b57c24519
--- /dev/null
+++ b/src/hooks/compaction-context-injector/constants.ts
@@ -0,0 +1,5 @@
+export const HOOK_NAME = "compaction-context-injector"
+export const AGENT_RECOVERY_PROMPT = "[restore checkpointed session agent configuration after compaction]"
+export const NO_TEXT_TAIL_THRESHOLD = 5
+export const RECOVERY_COOLDOWN_MS = 60_000
+export const RECENT_COMPACTION_WINDOW_MS = 10 * 60 * 1000
diff --git a/src/hooks/compaction-context-injector/hook.ts b/src/hooks/compaction-context-injector/hook.ts
index 81857e12f..462dc18a6 100644
--- a/src/hooks/compaction-context-injector/hook.ts
+++ b/src/hooks/compaction-context-injector/hook.ts
@@ -1,70 +1,15 @@
 import type { BackgroundManager } from "../../features/background-agent"
-import { updateSessionAgent } from "../../features/claude-code-session-state"
 import {
   clearCompactionAgentConfigCheckpoint,
-  getCompactionAgentConfigCheckpoint,
   setCompactionAgentConfigCheckpoint,
 } from "../../shared/compaction-agent-config-checkpoint"
-import { createInternalAgentTextPart } from "../../shared/internal-initiator-marker"
 import { log } from "../../shared/logger"
-import { setSessionModel } from "../../shared/session-model-state"
-import { setSessionTools } from "../../shared/session-tools-store"
 import { COMPACTION_CONTEXT_PROMPT } from "./compaction-context-prompt"
-import {
-  createExpectedRecoveryPromptConfig,
-  isPromptConfigRecovered,
-} from "./recovery-prompt-config"
-import {
-  resolveLatestSessionPromptConfig,
-  resolveSessionPromptConfig,
-} from "./session-prompt-config-resolver"
-import {
-  finalizeTrackedAssistantMessage,
-  shouldTreatAssistantPartAsOutput,
-  trackAssistantOutput,
-  type TailMonitorState,
-} from "./tail-monitor"
-
-const HOOK_NAME = "compaction-context-injector"
-const AGENT_RECOVERY_PROMPT = "[restore checkpointed session agent configuration after compaction]"
-const NO_TEXT_TAIL_THRESHOLD = 5
-const RECOVERY_COOLDOWN_MS = 60_000
-const RECENT_COMPACTION_WINDOW_MS = 10 * 60 * 1000
-
-type CompactionContextClient = {
-  client: {
-    session: {
-      messages: (input: { path: { id: string } }) => Promise<unknown>
-      promptAsync: (input: {
-        path: { id: string }
-        body: {
-          noReply?: boolean
-          agent?: string
-          model?: { providerID: string; modelID: string }
-          tools?: Record<string, boolean>
-          parts: Array<{ type: "text"; text: string }>
-        }
-        query?: { directory: string }
-      }) => Promise<unknown>
-    }
-  }
-  directory: string
-}
-
-export interface CompactionContextInjector {
-  capture: (sessionID: string) => Promise<void>
-  inject: (sessionID?: string) => string
-  event: (input: { event: { type: string; properties?: unknown } }) => Promise<void>
-}
-
-function isCompactionAgent(agent: string | undefined): boolean {
-  return agent?.trim().toLowerCase() === "compaction"
-}
-
-function resolveSessionID(props?: Record<string, unknown>): string | undefined {
-  return (props?.sessionID ??
-    (props?.info as { id?: string } | undefined)?.id) as string | undefined
-}
+import { resolveSessionPromptConfig } from "./session-prompt-config-resolver"
+import { finalizeTrackedAssistantMessage, shouldTreatAssistantPartAsOutput, trackAssistantOutput, type TailMonitorState } from "./tail-monitor"
+import { resolveSessionID } from "./session-id"
+import type { CompactionContextClient, CompactionContextInjector } from "./types"
+import { createRecoveryLogic } from "./recovery"
 
 export function createCompactionContextInjector(options?: {
   ctx?: CompactionContextClient
@@ -88,119 +33,7 @@ export function createCompactionContextInjector(options?: {
     return created
   }
 
-  const recoverCheckpointedAgentConfig = async (
-    sessionID: string,
-    reason: "session.compacted" | "no-text-tail",
-  ): Promise<boolean> => {
-    if (!ctx) {
-      return false
-    }
-
-    const checkpoint = getCompactionAgentConfigCheckpoint(sessionID)
-    if (!checkpoint?.agent) {
-      return false
-    }
-    const checkpointWithAgent = {
-      ...checkpoint,
-      agent: checkpoint.agent,
-    }
-
-    const tailState = getTailState(sessionID)
-    const now = Date.now()
-    if (tailState.lastRecoveryAt && now - tailState.lastRecoveryAt < RECOVERY_COOLDOWN_MS) {
-      return false
-    }
-
-    const currentPromptConfig = await resolveSessionPromptConfig(ctx, sessionID)
-    const expectedPromptConfig = createExpectedRecoveryPromptConfig(
-      checkpointWithAgent,
-      currentPromptConfig,
-    )
-    const model = expectedPromptConfig.model
-    const tools = expectedPromptConfig.tools
-
-    if (reason === "session.compacted") {
-      const latestPromptConfig = await resolveLatestSessionPromptConfig(ctx, sessionID)
-      if (isPromptConfigRecovered(latestPromptConfig, expectedPromptConfig)) {
-        return false
-      }
-    }
-
-    try {
-      await ctx.client.session.promptAsync({
-        path: { id: sessionID },
-        body: {
-          noReply: true,
-          agent: expectedPromptConfig.agent,
-          ...(model ? { model } : {}),
-          ...(tools ? { tools } : {}),
-          parts: [createInternalAgentTextPart(AGENT_RECOVERY_PROMPT)],
-        },
-        query: { directory: ctx.directory },
-      })
-
-      const recoveredPromptConfig = await resolveLatestSessionPromptConfig(ctx, sessionID)
-      if (!isPromptConfigRecovered(recoveredPromptConfig, expectedPromptConfig)) {
-        log(`[${HOOK_NAME}] Re-injected agent config but recovery is still incomplete`, {
-          sessionID,
-          reason,
-          agent: expectedPromptConfig.agent,
-          model,
-          hasTools: !!tools,
-          recoveredPromptConfig,
-        })
-        return false
-      }
-
-      updateSessionAgent(sessionID, expectedPromptConfig.agent)
-      if (model) {
-        setSessionModel(sessionID, model)
-      }
-      if (tools) {
-        setSessionTools(sessionID, tools)
-      }
-
-      tailState.lastRecoveryAt = now
-      tailState.consecutiveNoTextMessages = 0
-
-      log(`[${HOOK_NAME}] Re-injected checkpointed agent config`, {
-        sessionID,
-        reason,
-        agent: expectedPromptConfig.agent,
-        model,
-      })
-
-      return true
-    } catch (error) {
-      log(`[${HOOK_NAME}] Failed to re-inject checkpointed agent config`, {
-        sessionID,
-        reason,
-        error: String(error),
-      })
-      return false
-    }
-  }
-
-  const maybeWarnAboutNoTextTail = async (sessionID: string): Promise<void> => {
-    const tailState = getTailState(sessionID)
-    if (tailState.consecutiveNoTextMessages < NO_TEXT_TAIL_THRESHOLD) {
-      return
-    }
-
-    const recentlyCompacted =
-      tailState.lastCompactedAt !== undefined &&
-      Date.now() - tailState.lastCompactedAt < RECENT_COMPACTION_WINDOW_MS
-
-    log(`[${HOOK_NAME}] Detected consecutive assistant messages with no text`, {
-      sessionID,
-      consecutiveNoTextMessages: tailState.consecutiveNoTextMessages,
-      recentlyCompacted,
-    })
-
-    if (recentlyCompacted) {
-      await recoverCheckpointedAgentConfig(sessionID, "no-text-tail")
-    }
-  }
+  const { recoverCheckpointedAgentConfig, maybeWarnAboutNoTextTail } = createRecoveryLogic(ctx, getTailState)
 
   const capture = async (sessionID: string): Promise<void> => {
     if (!ctx || !sessionID) {
@@ -213,7 +46,7 @@ export function createCompactionContextInjector(options?: {
     }
 
     setCompactionAgentConfigCheckpoint(sessionID, promptConfig)
-    log(`[${HOOK_NAME}] Captured agent checkpoint before compaction`, {
+    log(`[compaction-context-injector] Captured agent checkpoint before compaction`, {
       sessionID,
       agent: promptConfig.agent,
       model: promptConfig.model,
diff --git a/src/hooks/compaction-context-injector/recovery.ts b/src/hooks/compaction-context-injector/recovery.ts
new file mode 100644
index 000000000..9542d6e17
--- /dev/null
+++ b/src/hooks/compaction-context-injector/recovery.ts
@@ -0,0 +1,143 @@
+import { updateSessionAgent } from "../../features/claude-code-session-state"
+import {
+  getCompactionAgentConfigCheckpoint,
+} from "../../shared/compaction-agent-config-checkpoint"
+import { createInternalAgentTextPart } from "../../shared/internal-initiator-marker"
+import { log } from "../../shared/logger"
+import { setSessionModel } from "../../shared/session-model-state"
+import { setSessionTools } from "../../shared/session-tools-store"
+import {
+  createExpectedRecoveryPromptConfig,
+  isPromptConfigRecovered,
+} from "./recovery-prompt-config"
+import {
+  resolveLatestSessionPromptConfig,
+  resolveSessionPromptConfig,
+} from "./session-prompt-config-resolver"
+import { AGENT_RECOVERY_PROMPT, NO_TEXT_TAIL_THRESHOLD, RECOVERY_COOLDOWN_MS, RECENT_COMPACTION_WINDOW_MS } from "./constants"
+import type { CompactionContextClient } from "./types"
+import type { TailMonitorState } from "./tail-monitor"
+
+export function createRecoveryLogic(
+  ctx: CompactionContextClient | undefined,
+  getTailState: (sessionID: string) => TailMonitorState,
+) {
+  const recoverCheckpointedAgentConfig = async (
+    sessionID: string,
+    reason: "session.compacted" | "no-text-tail",
+  ): Promise<boolean> => {
+    if (!ctx) {
+      return false
+    }
+
+    const checkpoint = getCompactionAgentConfigCheckpoint(sessionID)
+    if (!checkpoint?.agent) {
+      return false
+    }
+    const checkpointWithAgent = {
+      ...checkpoint,
+      agent: checkpoint.agent,
+    }
+
+    const tailState = getTailState(sessionID)
+    const now = Date.now()
+    if (tailState.lastRecoveryAt && now - tailState.lastRecoveryAt < RECOVERY_COOLDOWN_MS) {
+      return false
+    }
+
+    const currentPromptConfig = await resolveSessionPromptConfig(ctx, sessionID)
+    const expectedPromptConfig = createExpectedRecoveryPromptConfig(
+      checkpointWithAgent,
+      currentPromptConfig,
+    )
+    const model = expectedPromptConfig.model
+    const tools = expectedPromptConfig.tools
+
+    if (reason === "session.compacted") {
+      const latestPromptConfig = await resolveLatestSessionPromptConfig(ctx, sessionID)
+      if (isPromptConfigRecovered(latestPromptConfig, expectedPromptConfig)) {
+        return false
+      }
+    }
+
+    try {
+      await ctx.client.session.promptAsync({
+        path: { id: sessionID },
+        body: {
+          noReply: true,
+          agent: expectedPromptConfig.agent,
+          ...(model ? { model } : {}),
+          ...(tools ? { tools } : {}),
+          parts: [createInternalAgentTextPart(AGENT_RECOVERY_PROMPT)],
+        },
+        query: { directory: ctx.directory },
+      })
+
+      const recoveredPromptConfig = await resolveLatestSessionPromptConfig(ctx, sessionID)
+      if (!isPromptConfigRecovered(recoveredPromptConfig, expectedPromptConfig)) {
+        log(`[compaction-context-injector] Re-injected agent config but recovery is still incomplete`, {
+          sessionID,
+          reason,
+          agent: expectedPromptConfig.agent,
+          model,
+          hasTools: !!tools,
+          recoveredPromptConfig,
+        })
+        return false
+      }
+
+      updateSessionAgent(sessionID, expectedPromptConfig.agent)
+      if (model) {
+        setSessionModel(sessionID, model)
+      }
+      if (tools) {
+        setSessionTools(sessionID, tools)
+      }
+
+      tailState.lastRecoveryAt = now
+      tailState.consecutiveNoTextMessages = 0
+
+      log(`[compaction-context-injector] Re-injected checkpointed agent config`, {
+        sessionID,
+        reason,
+        agent: expectedPromptConfig.agent,
+        model,
+      })
+
+      return true
+    } catch (error) {
+      log(`[compaction-context-injector] Failed to re-inject checkpointed agent config`, {
+        sessionID,
+        reason,
+        error: String(error),
+      })
+      return false
+    }
+  }
+
+  const maybeWarnAboutNoTextTail = async (sessionID: string): Promise<void> => {
+    const tailState = getTailState(sessionID)
+    if (tailState.consecutiveNoTextMessages < NO_TEXT_TAIL_THRESHOLD) {
+      return
+    }
+
+    const recentlyCompacted =
+      tailState.lastCompactedAt !== undefined &&
+      Date.now() - tailState.lastCompactedAt < RECENT_COMPACTION_WINDOW_MS
+
+    log(`[compaction-context-injector] Detected consecutive assistant messages with no text`, {
+      sessionID,
+      consecutiveNoTextMessages: tailState.consecutiveNoTextMessages,
+      recentlyCompacted,
+    })
+
+    if (recentlyCompacted) {
+      await recoverCheckpointedAgentConfig(sessionID, "no-text-tail")
+    }
+  }
+
+  return {
+    recoverCheckpointedAgentConfig,
+    maybeWarnAboutNoTextTail,
+  }
+}
diff --git a/src/hooks/compaction-context-injector/session-id.ts b/src/hooks/compaction-context-injector/session-id.ts
new file mode 100644
index 000000000..29de9c5c4
--- /dev/null
+++ b/src/hooks/compaction-context-injector/session-id.ts
@@ -0,0 +1,8 @@
+export function isCompactionAgent(agent: string | undefined): boolean {
+  return agent?.trim().toLowerCase() === "compaction"
+}
+
+export function resolveSessionID(props?: Record<string, unknown>): string | undefined {
+  return (props?.sessionID ??
+    (props?.info as { id?: string } | undefined)?.id) as string | undefined
+}
diff --git a/src/hooks/compaction-context-injector/types.ts b/src/hooks/compaction-context-injector/types.ts
new file mode 100644
index 000000000..b97c2e6f6
--- /dev/null
+++ b/src/hooks/compaction-context-injector/types.ts
@@ -0,0 +1,25 @@
+export interface CompactionContextInjector {
+  capture: (sessionID: string) => Promise<void>
+  inject: (sessionID?: string) => string
+  event: (input: { event: { type: string; properties?: unknown } }) => Promise<void>
+}
+
+export type CompactionContextClient = {
+  client: {
+    session: {
+      messages: (input: { path: { id: string } }) => Promise<unknown>
+      promptAsync: (input: {
+        path: { id: string }
+        body: {
+          noReply?: boolean
+          agent?: string
+          model?: { providerID: string; modelID: string }
+          tools?: Record<string, boolean>
+          parts: Array<{ type: "text"; text: string }>
+        }
+        query?: { directory: string }
+      }) => Promise<unknown>
+    }
+  }
+  directory: string
+}