Session resume permanently broken: tool_use/tool_result mismatch from interleaved sub-agent turns

## Bug Description

After resuming a session that used multi-agent (sub-agent) parallel execution, every prompt fails with:

```
CAPIError: 400 messages.9: `tool_use` ids were found without `tool_result` blocks immediately after: tooluse_KnoMQcLpsPRnvfH4stPa5s.
Each `tool_use` block must have a corresponding `tool_result` block in the next message.
```

The session is **permanently unrecoverable** — the error persists across retries, resumes, and even CLI version upgrades (tested 1.0.10 → 1.0.12-1).

## Root Cause Analysis

The conversation reconstruction from `events.jsonl` on resume cannot handle tool_results that complete **after** a sub-agent turn has interleaved. The events are recorded faithfully, but the reconstructed `messages[]` array violates Claude's tool_use/tool_result adjacency requirement.

### Event sequence from events.jsonl (lines 1947–1967):

1. **Line 1947**: Main agent (Claude, `tooluse_*` IDs) emits `assistant.message` with 3 parallel tool_use requests
2. **Line 1953**: 1st tool completes (`tooluse_jUS9...`)
3. **Line 1954**: A **sub-agent turn** begins — new `assistant.message` with `call_*` IDs (OpenAI format), turnId=1
4. **Line 1960**: 2nd tool from main agent completes (`tooluse_EBk...`)
5. **Line 1961**: Sub-agent tools complete
6. **Line 1963**: `assistant.turn_end` turnId=1 (sub-agent done)
7. **Line 1966**: 3rd tool from main agent completes (`tooluse_KnoMQcL...`) — **arrives after sub-agent turn**
8. **Line 1967**: `assistant.turn_end` turnId=0 (main done)

On resume, the conversation builder places the sub-agent's assistant message (line 1954) between the main agent's tool_use (line 1947) and the tool_result for `tooluse_KnoMQcL...` (line 1966). This violates the API requirement that every `tool_use` must have a `tool_result` in the immediately next message.

## Impact

- Session is permanently broken — no recovery path exists
- User loses all conversation context (this was a long session with 2700+ events)
- Error is deterministic: always fails at `messages.9`
- Affects any session that had parallel tool calls where a sub-agent turn interleaved before all tool_results arrived

## Reproduction

- Session ID: `0c90fe17-4e2d-4bf6-8126-bcf97750e74c`
- CLI versions tested: `darwin-arm64/1.0.10`, `universal/1.0.12-1`
- 4+ failed attempts across 3 separate resume cycles

## Suggested Fixes

1. **Conversation builder**: Group all tool_results with their originating tool_use message regardless of interleaved sub-agent turns
2. **Graceful degradation**: Detect orphaned tool_use blocks and inject synthetic tool_results (e.g., `"[tool result unavailable after session resume]"`) rather than sending a malformed conversation
3. **Error recovery**: Detect this specific 400 error pattern and auto-truncate the conversation before the corrupted point

## Contact

Please reach out to **@PureWeen** (Shane Neuville) for the full `events.jsonl` file for debugging. He has the complete session state available.

Inizia riproducendo il fallimento della ripresa con la sessione 0c90fe17-4e2d-4bf6-8126-bcf97750e74c e ispeziona le righe 1947–1967 di events.jsonl insieme al costruttore della conversazione. Traccia come il turno intercalato del sub-agent viene inserito tra il tool_use e il tool_result dello strumento principale. Il lavoro è completato quando le sessioni riprese mantengono un’adjacency valida tra tool_use/tool_result oppure recuperano correttamente invece di inviare la conversazione malformata.

Scritto dal modello di indicizzazione a partire dal testo della issue.