| 47 | } |
| 48 | |
| 49 | export function deriveNextReplMessageSignalState( |
| 50 | previous: ReplMessageSignalState | null, |
| 51 | messages: Message[], |
| 52 | isLoading: boolean, |
| 53 | ): ReplMessageSignalState { |
| 54 | if (!previous) { |
| 55 | return deriveReplMessageSignalState(messages, isLoading) |
| 56 | } |
| 57 | |
| 58 | if (messages.length === previous.messageCount) { |
| 59 | const lastMessageRef = messages.at(-1) |
| 60 | if (lastMessageRef === previous.lastMessageRef) { |
| 61 | return withSignals(previous, isLoading) |
| 62 | } |
| 63 | |
| 64 | // Fast path: only the last message changed. If both old and new last |
| 65 | // messages are non-assistant, all previous signal values remain valid |
| 66 | // (most common: ephemeral progress updates replacing a progress message). |
| 67 | // If the new last message is an assistant, recompute signals from it. |
| 68 | // Otherwise fall back to full rebuild. |
| 69 | const oldLastWasAssistant = previous.lastMessageRef?.type === 'assistant' |
| 70 | const newLastIsAssistant = lastMessageRef?.type === 'assistant' |
| 71 | if (!oldLastWasAssistant && !newLastIsAssistant) { |
| 72 | return finalizeReplMessageSignalState( |
| 73 | messages, |
| 74 | previous.promptSignals, |
| 75 | previous.lastAssistantToolUses, |
| 76 | previous.stopHookState, |
| 77 | isLoading, |
| 78 | ) |
| 79 | } |
| 80 | if (newLastIsAssistant && lastMessageRef) { |
| 81 | const promptSignals = applyAppendedPromptSignals( |
| 82 | previous.promptSignals, |
| 83 | [lastMessageRef], |
| 84 | ) |
| 85 | const lastAssistantToolUses = applyAppendedLastAssistantToolUses( |
| 86 | previous.lastAssistantToolUses, |
| 87 | [lastMessageRef], |
| 88 | ) |
| 89 | return finalizeReplMessageSignalState( |
| 90 | messages, |
| 91 | promptSignals, |
| 92 | lastAssistantToolUses, |
| 93 | previous.stopHookState, |
| 94 | isLoading, |
| 95 | ) |
| 96 | } |
| 97 | } |
| 98 | |
| 99 | if (canAppendIncrementally(previous, messages)) { |
| 100 | const appended = messages.slice(previous.messageCount) |
| 101 | const promptSignals = applyAppendedPromptSignals( |
| 102 | previous.promptSignals, |
| 103 | appended, |
| 104 | ) |
| 105 | const lastAssistantToolUses = applyAppendedLastAssistantToolUses( |
| 106 | previous.lastAssistantToolUses, |