feat: history truncation + lazy message rehydrate (daemon + IPC)

[ashleeradka]

Summary

Add server-side text and tool result truncation to history responses, plus a new message_content_request endpoint for on-demand full-content retrieval. This is the daemon/IPC foundation for client-side memory optimization — clients can now request lightweight history (truncated text, no heavy payloads) and fetch full content only when needed.

Implementation

IPC Contract Changes (ipc-contract/sessions.ts)

• HistoryRequest: Added maxTextChars and maxToolResultChars optional fields for server-side truncation
• New MessageContentRequest / MessageContentResponse message types for single-message full-content fetch
• HistoryResponse messages: Added wasTruncated boolean flag

Server Handler (handlers/sessions.ts)

• handleHistoryRequest: Applies text truncation (maxTextChars) and tool result truncation (maxToolResultChars) with … [truncated] suffix. Sets wasTruncated: true on affected messages.
• New handleMessageContentRequest: Fetches a single message by ID from the conversation store, parses and renders its content (text + tool calls), returns full untruncated data.

Data Layer (conversation-store.ts)

• Added getMessageById(messageId, conversationId?) for efficient single-message lookup.

Generated Types (IPCContractGenerated.swift)

• Auto-generated Swift types for all new IPC fields: IPCMessageContentRequest, IPCMessageContentResponse, IPCMessageContentResponseToolCall, plus updated IPCHistoryRequest and IPCHistoryResponseMessage.

Files Changed

• assistant/src/daemon/ipc-contract/sessions.ts — contract extensions
• assistant/src/daemon/handlers/sessions.ts — truncation logic + new handler
• assistant/src/memory/conversation-store.ts — getMessageById
• assistant/src/daemon/ipc-contract-inventory.json — new message types
• assistant/src/__tests__/ipc-snapshot.test.ts — test fixtures
• assistant/src/__tests__/__snapshots__/ipc-snapshot.test.ts.snap — updated snapshots
• clients/shared/IPC/Generated/IPCContractGenerated.swift — regenerated Swift types

Testing

• IPC snapshot tests updated with fixtures for new message types
• Manual: send history_request with maxTextChars: 100 → verify truncated text with wasTruncated: true
• Manual: send message_content_request for a truncated message → verify full content returned

Context

Part of the text-retention-fix blitz (epic #9272). M1 of 5 milestones.
Closes #9273

🤖 Generated with Claude Code

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[devin-ai-integration]

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[chatgpt-codex-connector]

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[ashleeradka]

Addressed in #9315