fix(compaction): validate recovered agent config state

Retry compaction recovery when model or tool state is still incomplete, and treat reasoning or tool-only assistant progress as valid output so no-text tail recovery does not misfire.

src/hooks/compaction-context-injector/compaction-context-prompt.ts

@@ -0,0 +1,56 @@
+import {
+  createSystemDirective,
+  SystemDirectiveTypes,
+} from "../../shared/system-directive"
+
+export const COMPACTION_CONTEXT_PROMPT = `${createSystemDirective(SystemDirectiveTypes.COMPACTION_CONTEXT)}
+
+When summarizing this session, you MUST include the following sections in your summary:
+
+## 1. User Requests (As-Is)
+- List all original user requests exactly as they were stated
+- Preserve the user's exact wording and intent
+
+## 2. Final Goal
+- What the user ultimately wanted to achieve
+- The end result or deliverable expected
+
+## 3. Work Completed
+- What has been done so far
+- Files created/modified
+- Features implemented
+- Problems solved
+
+## 4. Remaining Tasks
+- What still needs to be done
+- Pending items from the original request
+- Follow-up tasks identified during the work
+
+## 5. Active Working Context (For Seamless Continuation)
+- **Files**: Paths of files currently being edited or frequently referenced
+- **Code in Progress**: Key code snippets, function signatures, or data structures under active development
+- **External References**: Documentation URLs, library APIs, or external resources being consulted
+- **State & Variables**: Important variable names, configuration values, or runtime state relevant to ongoing work
+
+## 6. Explicit Constraints (Verbatim Only)
+- Include ONLY constraints explicitly stated by the user or in existing AGENTS.md context
+- Quote constraints verbatim (do not paraphrase)
+- Do NOT invent, add, or modify constraints
+- If no explicit constraints exist, write "None"
+
+## 7. Agent Verification State (Critical for Reviewers)
+- **Current Agent**: What agent is running (momus, oracle, etc.)
+- **Verification Progress**: Files already verified/validated
+- **Pending Verifications**: Files still needing verification
+- **Previous Rejections**: If reviewer agent, what was rejected and why
+- **Acceptance Status**: Current state of review process
+
+This section is CRITICAL for reviewer agents (momus, oracle) to maintain continuity.
+
+## 8. Delegated Agent Sessions
+- List ALL background agent tasks spawned during this session
+- For each: agent name, category, status, description, and **session_id**
+- **RESUME, DON'T RESTART.** Each listed session retains full context. After compaction, use \`session_id\` to continue existing agent sessions instead of spawning new ones. This saves tokens, preserves learned context, and prevents duplicate work.
+
+This context is critical for maintaining continuity after compaction.
+`

src/hooks/compaction-context-injector/hook.ts

@@ -9,14 +9,21 @@ import { createInternalAgentTextPart } from "../../shared/internal-initiator-mar
 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 {
-  createSystemDirective,
-  SystemDirectiveTypes,
-} from "../../shared/system-directive"
+  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]"
@@ -44,14 +51,6 @@ type CompactionContextClient = {
   directory: string
 }
 
-type TailMonitorState = {
-  currentMessageID?: string
-  currentHasText: boolean
-  consecutiveNoTextMessages: number
-  lastCompactedAt?: number
-  lastRecoveryAt?: number
-}
-
 export interface CompactionContextInjector {
   capture: (sessionID: string) => Promise<void>
   inject: (sessionID?: string) => string
@@ -67,81 +66,6 @@ function resolveSessionID(props?: Record<string, unknown>): string | undefined {
     (props?.info as { id?: string } | undefined)?.id) as string | undefined
 }
 
-function finalizeTrackedAssistantMessage(state: TailMonitorState): number {
-  if (!state.currentMessageID) {
-    return state.consecutiveNoTextMessages
-  }
-
-  state.consecutiveNoTextMessages = state.currentHasText
-    ? 0
-    : state.consecutiveNoTextMessages + 1
-  state.currentMessageID = undefined
-  state.currentHasText = false
-
-  return state.consecutiveNoTextMessages
-}
-
-function trackAssistantText(state: TailMonitorState, messageID?: string): void {
-  if (messageID && !state.currentMessageID) {
-    state.currentMessageID = messageID
-  }
-
-  state.currentHasText = true
-  state.consecutiveNoTextMessages = 0
-}
-
-const COMPACTION_CONTEXT_PROMPT = `${createSystemDirective(SystemDirectiveTypes.COMPACTION_CONTEXT)}
-
-When summarizing this session, you MUST include the following sections in your summary:
-
-## 1. User Requests (As-Is)
-- List all original user requests exactly as they were stated
-- Preserve the user's exact wording and intent
-
-## 2. Final Goal
-- What the user ultimately wanted to achieve
-- The end result or deliverable expected
-
-## 3. Work Completed
-- What has been done so far
-- Files created/modified
-- Features implemented
-- Problems solved
-
-## 4. Remaining Tasks
-- What still needs to be done
-- Pending items from the original request
-- Follow-up tasks identified during the work
-
-## 5. Active Working Context (For Seamless Continuation)
-- **Files**: Paths of files currently being edited or frequently referenced
-- **Code in Progress**: Key code snippets, function signatures, or data structures under active development
-- **External References**: Documentation URLs, library APIs, or external resources being consulted
-- **State & Variables**: Important variable names, configuration values, or runtime state relevant to ongoing work
-
-## 6. Explicit Constraints (Verbatim Only)
-- Include ONLY constraints explicitly stated by the user or in existing AGENTS.md context
-- Quote constraints verbatim (do not paraphrase)
-- Do NOT invent, add, or modify constraints
-- If no explicit constraints exist, write "None"
-
-## 7. Agent Verification State (Critical for Reviewers)
-- **Current Agent**: What agent is running (momus, oracle, etc.)
-- **Verification Progress**: Files already verified/validated
-- **Pending Verifications**: Files still needing verification
-- **Previous Rejections**: If reviewer agent, what was rejected and why
-- **Acceptance Status**: Current state of review process
-
-This section is CRITICAL for reviewer agents (momus, oracle) to maintain continuity.
-
-## 8. Delegated Agent Sessions
-- List ALL background agent tasks spawned during this session
-- For each: agent name, category, status, description, and **session_id**
-- **RESUME, DON'T RESTART.** Each listed session retains full context. After compaction, use \`session_id\` to continue existing agent sessions instead of spawning new ones. This saves tokens, preserves learned context, and prevents duplicate work.
-
-This context is critical for maintaining continuity after compaction.
-`
-
 export function createCompactionContextInjector(options?: {
   ctx?: CompactionContextClient
   backgroundManager?: BackgroundManager
@@ -157,7 +81,7 @@ export function createCompactionContextInjector(options?: {
     }
 
     const created: TailMonitorState = {
-      currentHasText: false,
+      currentHasOutput: false,
       consecutiveNoTextMessages: 0,
     }
     tailStates.set(sessionID, created)
@@ -176,6 +100,10 @@ export function createCompactionContextInjector(options?: {
     if (!checkpoint?.agent) {
       return false
     }
+    const checkpointWithAgent = {
+      ...checkpoint,
+      agent: checkpoint.agent,
+    }
 
     const tailState = getTailState(sessionID)
     const now = Date.now()
@@ -183,28 +111,27 @@ export function createCompactionContextInjector(options?: {
       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)
-      const latestAgentMatchesCheckpoint =
-        typeof latestPromptConfig.agent === "string" &&
-        latestPromptConfig.agent.toLowerCase() === checkpoint.agent.toLowerCase() &&
-        !isCompactionAgent(latestPromptConfig.agent)
-
-      if (latestAgentMatchesCheckpoint && latestPromptConfig.model) {
+      if (isPromptConfigRecovered(latestPromptConfig, expectedPromptConfig)) {
         return false
       }
     }
 
-    const currentPromptConfig = await resolveSessionPromptConfig(ctx, sessionID)
-    const model = checkpoint.model ?? currentPromptConfig.model
-    const tools = checkpoint.tools ?? currentPromptConfig.tools
-
     try {
       await ctx.client.session.promptAsync({
         path: { id: sessionID },
         body: {
           noReply: true,
-          agent: checkpoint.agent,
+          agent: expectedPromptConfig.agent,
           ...(model ? { model } : {}),
           ...(tools ? { tools } : {}),
           parts: [createInternalAgentTextPart(AGENT_RECOVERY_PROMPT)],
@@ -212,7 +139,20 @@ export function createCompactionContextInjector(options?: {
         query: { directory: ctx.directory },
       })
 
-      updateSessionAgent(sessionID, checkpoint.agent)
+      const recoveredPromptConfig = await resolveLatestSessionPromptConfig(ctx, sessionID)
+      if (!isPromptConfigRecovered(recoveredPromptConfig, expectedPromptConfig)) {
+        log(`[${HOOK_NAME}] Re-injected agent config but recovery is still incomplete`, {
+          sessionID,
+          reason,
+          agent: expectedPromptConfig.agent,
+          model,
+          hasTools: !!tools,
+          recoveredPromptConfig,
+        })
+        return false
+      }
+
+      updateSessionAgent(sessionID, expectedPromptConfig.agent)
       if (model) {
         setSessionModel(sessionID, model)
       }
@@ -226,7 +166,7 @@ export function createCompactionContextInjector(options?: {
       log(`[${HOOK_NAME}] Re-injected checkpointed agent config`, {
         sessionID,
         reason,
-        agent: checkpoint.agent,
+        agent: expectedPromptConfig.agent,
         model,
       })
 
@@ -352,7 +292,7 @@ export function createCompactionContextInjector(options?: {
 
       if (tailState.currentMessageID !== info.id) {
         tailState.currentMessageID = info.id
-        tailState.currentHasText = false
+        tailState.currentHasOutput = false
       }
       return
     }
@@ -367,7 +307,7 @@ export function createCompactionContextInjector(options?: {
         return
       }
 
-      trackAssistantText(getTailState(sessionID), messageID)
+      trackAssistantOutput(getTailState(sessionID), messageID)
       return
     }
 
@@ -379,11 +319,11 @@ export function createCompactionContextInjector(options?: {
         text?: string
       } | undefined
 
-      if (!part?.sessionID || part.type !== "text" || !part.text?.trim()) {
+      if (!part?.sessionID || !shouldTreatAssistantPartAsOutput(part)) {
         return
       }
 
-      trackAssistantText(getTailState(part.sessionID), part.messageID)
+      trackAssistantOutput(getTailState(part.sessionID), part.messageID)
     }
   }
 

src/hooks/compaction-context-injector/recovery-prompt-config.ts

@@ -0,0 +1,76 @@
+import type { CompactionAgentConfigCheckpoint } from "../../shared/compaction-agent-config-checkpoint"
+
+export type RecoveryPromptConfig = CompactionAgentConfigCheckpoint & {
+  agent: string
+}
+
+function isCompactionAgent(agent: string | undefined): boolean {
+  return agent?.trim().toLowerCase() === "compaction"
+}
+
+function matchesExpectedModel(
+  actualModel: CompactionAgentConfigCheckpoint["model"],
+  expectedModel: CompactionAgentConfigCheckpoint["model"],
+): boolean {
+  if (!expectedModel) {
+    return true
+  }
+
+  return (
+    actualModel?.providerID === expectedModel.providerID &&
+    actualModel.modelID === expectedModel.modelID
+  )
+}
+
+function matchesExpectedTools(
+  actualTools: CompactionAgentConfigCheckpoint["tools"],
+  expectedTools: CompactionAgentConfigCheckpoint["tools"],
+): boolean {
+  if (!expectedTools) {
+    return true
+  }
+
+  if (!actualTools) {
+    return false
+  }
+
+  const expectedEntries = Object.entries(expectedTools)
+  if (expectedEntries.length !== Object.keys(actualTools).length) {
+    return false
+  }
+
+  return expectedEntries.every(
+    ([toolName, isAllowed]) => actualTools[toolName] === isAllowed,
+  )
+}
+
+export function createExpectedRecoveryPromptConfig(
+  checkpoint: Pick<RecoveryPromptConfig, "agent"> & CompactionAgentConfigCheckpoint,
+  currentPromptConfig: CompactionAgentConfigCheckpoint,
+): RecoveryPromptConfig {
+  const model = checkpoint.model ?? currentPromptConfig.model
+  const tools = checkpoint.tools ?? currentPromptConfig.tools
+
+  return {
+    agent: checkpoint.agent,
+    ...(model ? { model } : {}),
+    ...(tools ? { tools } : {}),
+  }
+}
+
+export function isPromptConfigRecovered(
+  actualPromptConfig: CompactionAgentConfigCheckpoint,
+  expectedPromptConfig: RecoveryPromptConfig,
+): boolean {
+  const actualAgent = actualPromptConfig.agent
+  const agentMatches =
+    typeof actualAgent === "string" &&
+    !isCompactionAgent(actualAgent) &&
+    actualAgent.toLowerCase() === expectedPromptConfig.agent.toLowerCase()
+
+  return (
+    agentMatches &&
+    matchesExpectedModel(actualPromptConfig.model, expectedPromptConfig.model) &&
+    matchesExpectedTools(actualPromptConfig.tools, expectedPromptConfig.tools)
+  )
+}

src/hooks/compaction-context-injector/recovery.test.ts

@@ -0,0 +1,294 @@
+/// <reference path="../../../bun-test.d.ts" />
+
+import { describe, expect, it } from "bun:test"
+import { createCompactionContextInjector } from "./index"
+
+type SessionMessageResponse = Array<{
+  info?: Record<string, unknown>
+}>
+
+type PromptAsyncInput = {
+  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 }
+}
+
+function createPromptAsyncRecorder(): {
+  calls: PromptAsyncInput[]
+  promptAsync: (input: PromptAsyncInput) => Promise<Record<string, never>>
+} {
+  const calls: PromptAsyncInput[] = []
+
+  return {
+    calls,
+    promptAsync: async (input: PromptAsyncInput) => {
+      calls.push(input)
+      return {}
+    },
+  }
+}
+
+function createMockContext(
+  messageResponses: SessionMessageResponse[],
+  promptAsync: (input: PromptAsyncInput) => Promise<Record<string, never>>,
+) {
+  let callIndex = 0
+
+  return {
+    client: {
+      session: {
+        messages: async () => {
+          const response =
+            messageResponses[Math.min(callIndex, messageResponses.length - 1)] ?? []
+          callIndex += 1
+          return { data: response }
+        },
+        promptAsync,
+      },
+    },
+    directory: "/tmp/test",
+  }
+}
+
+function createAssistantMessageUpdatedEvent(sessionID: string, messageID: string) {
+  return {
+    event: {
+      type: "message.updated",
+      properties: {
+        info: {
+          id: messageID,
+          role: "assistant",
+          sessionID,
+        },
+      },
+    },
+  } as const
+}
+
+function createMeaningfulPartUpdatedEvent(
+  sessionID: string,
+  messageID: string,
+  type: "reasoning" | "tool_use",
+) {
+  return {
+    event: {
+      type: "message.part.updated",
+      properties: {
+        part: {
+          messageID,
+          sessionID,
+          type,
+          ...(type === "reasoning" ? { text: "thinking" } : {}),
+        },
+      },
+    },
+  } as const
+}
+
+describe("createCompactionContextInjector recovery", () => {
+  it("re-injects after compaction when agent and model match but tools are missing", async () => {
+    //#given
+    const promptAsyncRecorder = createPromptAsyncRecorder()
+    const ctx = createMockContext(
+      [
+        [
+          {
+            info: {
+              role: "user",
+              agent: "atlas",
+              model: { providerID: "openai", modelID: "gpt-5" },
+              tools: { bash: true },
+            },
+          },
+        ],
+        [
+          {
+            info: {
+              role: "user",
+              agent: "atlas",
+              model: { providerID: "openai", modelID: "gpt-5" },
+            },
+          },
+        ],
+        [
+          {
+            info: {
+              role: "user",
+              agent: "atlas",
+              model: { providerID: "openai", modelID: "gpt-5" },
+            },
+          },
+        ],
+        [
+          {
+            info: {
+              role: "user",
+              agent: "atlas",
+              model: { providerID: "openai", modelID: "gpt-5" },
+              tools: { bash: true },
+            },
+          },
+        ],
+      ],
+      promptAsyncRecorder.promptAsync,
+    )
+    const injector = createCompactionContextInjector({ ctx })
+
+    //#when
+    await injector.capture("ses_missing_tools")
+    await injector.event({
+      event: { type: "session.compacted", properties: { sessionID: "ses_missing_tools" } },
+    })
+
+    //#then
+    expect(promptAsyncRecorder.calls.length).toBe(1)
+    expect(promptAsyncRecorder.calls[0]?.body.agent).toBe("atlas")
+    expect(promptAsyncRecorder.calls[0]?.body.model).toEqual({
+      providerID: "openai",
+      modelID: "gpt-5",
+    })
+    expect(promptAsyncRecorder.calls[0]?.body.tools).toEqual({ bash: true })
+  })
+
+  it("retries recovery when the recovered prompt config still mismatches expected model or tools", async () => {
+    //#given
+    const promptAsyncRecorder = createPromptAsyncRecorder()
+    const mismatchResponse = [
+      {
+        info: {
+          role: "user",
+          agent: "atlas",
+          model: { providerID: "openai", modelID: "gpt-4.1" },
+        },
+      },
+    ]
+    const ctx = createMockContext(
+      [
+        [
+          {
+            info: {
+              role: "user",
+              agent: "atlas",
+              model: { providerID: "openai", modelID: "gpt-5" },
+              tools: { bash: true },
+            },
+          },
+        ],
+        mismatchResponse,
+        mismatchResponse,
+        mismatchResponse,
+        mismatchResponse,
+        mismatchResponse,
+        mismatchResponse,
+      ],
+      promptAsyncRecorder.promptAsync,
+    )
+    const injector = createCompactionContextInjector({ ctx })
+
+    //#when
+    await injector.capture("ses_retry_incomplete_recovery")
+    await injector.event({
+      event: {
+        type: "session.compacted",
+        properties: { sessionID: "ses_retry_incomplete_recovery" },
+      },
+    })
+    await injector.event({
+      event: {
+        type: "session.compacted",
+        properties: { sessionID: "ses_retry_incomplete_recovery" },
+      },
+    })
+
+    //#then
+    expect(promptAsyncRecorder.calls.length).toBe(2)
+  })
+
+  it("does not treat reasoning-only assistant messages as a no-text tail", async () => {
+    //#given
+    const promptAsyncRecorder = createPromptAsyncRecorder()
+    const matchingPromptConfig = [
+      {
+        info: {
+          role: "user",
+          agent: "atlas",
+          model: { providerID: "openai", modelID: "gpt-5" },
+          tools: { bash: true },
+        },
+      },
+    ]
+    const ctx = createMockContext(
+      [matchingPromptConfig, matchingPromptConfig, matchingPromptConfig],
+      promptAsyncRecorder.promptAsync,
+    )
+    const injector = createCompactionContextInjector({ ctx })
+    const sessionID = "ses_reasoning_tail"
+
+    await injector.capture(sessionID)
+    await injector.event({
+      event: { type: "session.compacted", properties: { sessionID } },
+    })
+
+    //#when
+    for (let index = 1; index <= 5; index++) {
+      const messageID = `msg_reasoning_${index}`
+      await injector.event(createAssistantMessageUpdatedEvent(sessionID, messageID))
+      await injector.event(
+        createMeaningfulPartUpdatedEvent(sessionID, messageID, "reasoning"),
+      )
+      await injector.event({
+        event: { type: "session.idle", properties: { sessionID } },
+      })
+    }
+
+    //#then
+    expect(promptAsyncRecorder.calls.length).toBe(0)
+  })
+
+  it("does not treat tool_use-only assistant messages as a no-text tail", async () => {
+    //#given
+    const promptAsyncRecorder = createPromptAsyncRecorder()
+    const matchingPromptConfig = [
+      {
+        info: {
+          role: "user",
+          agent: "atlas",
+          model: { providerID: "openai", modelID: "gpt-5" },
+          tools: { bash: true },
+        },
+      },
+    ]
+    const ctx = createMockContext(
+      [matchingPromptConfig, matchingPromptConfig, matchingPromptConfig],
+      promptAsyncRecorder.promptAsync,
+    )
+    const injector = createCompactionContextInjector({ ctx })
+    const sessionID = "ses_tool_use_tail"
+
+    await injector.capture(sessionID)
+    await injector.event({
+      event: { type: "session.compacted", properties: { sessionID } },
+    })
+
+    //#when
+    for (let index = 1; index <= 5; index++) {
+      const messageID = `msg_tool_use_${index}`
+      await injector.event(createAssistantMessageUpdatedEvent(sessionID, messageID))
+      await injector.event(
+        createMeaningfulPartUpdatedEvent(sessionID, messageID, "tool_use"),
+      )
+      await injector.event({
+        event: { type: "session.idle", properties: { sessionID } },
+      })
+    }
+
+    //#then
+    expect(promptAsyncRecorder.calls.length).toBe(0)
+  })
+})

src/hooks/compaction-context-injector/tail-monitor.ts

@@ -0,0 +1,52 @@
+const MEANINGFUL_ASSISTANT_PART_TYPES = new Set([
+  "reasoning",
+  "tool",
+  "tool_use",
+])
+
+export type TailMonitorState = {
+  currentMessageID?: string
+  currentHasOutput: boolean
+  consecutiveNoTextMessages: number
+  lastCompactedAt?: number
+  lastRecoveryAt?: number
+}
+
+export function finalizeTrackedAssistantMessage(
+  state: TailMonitorState,
+): number {
+  if (!state.currentMessageID) {
+    return state.consecutiveNoTextMessages
+  }
+
+  state.consecutiveNoTextMessages = state.currentHasOutput
+    ? 0
+    : state.consecutiveNoTextMessages + 1
+  state.currentMessageID = undefined
+  state.currentHasOutput = false
+
+  return state.consecutiveNoTextMessages
+}
+
+export function shouldTreatAssistantPartAsOutput(part: {
+  type?: string
+  text?: string
+}): boolean {
+  if (part.type === "text") {
+    return !!part.text?.trim()
+  }
+
+  return typeof part.type === "string" && MEANINGFUL_ASSISTANT_PART_TYPES.has(part.type)
+}
+
+export function trackAssistantOutput(
+  state: TailMonitorState,
+  messageID?: string,
+): void {
+  if (messageID && !state.currentMessageID) {
+    state.currentMessageID = messageID
+  }
+
+  state.currentHasOutput = true
+  state.consecutiveNoTextMessages = 0
+}