Auto-retry on transient provider errors (overloaded, rate limit, 5xx)

- Add retry logic with exponential backoff (2s, 4s, 8s) in AgentSession
- Disable Anthropic SDK built-in retries (maxRetries: 0) to allow app-level handling
- TUI shows retry status with Escape to cancel
- RPC mode: add set_auto_retry, abort_retry commands and auto_retry_start/end events
- Configurable via settings.json: retry.enabled, retry.maxRetries, retry.baseDelayMs
- Exclude context overflow errors from retry (handled by compaction)

fixes #157

packages/coding-agent/CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ### Added
 
+- **Auto-retry on transient errors**: Automatically retries requests when providers return overloaded, rate limit, or server errors (429, 500, 502, 503, 504). Uses exponential backoff (2s, 4s, 8s). Shows retry status in TUI with option to cancel via Escape. Configurable in `settings.json` via `retry.enabled`, `retry.maxRetries`, `retry.baseDelayMs`. RPC mode emits `auto_retry_start` and `auto_retry_end` events. ([#157](https://github.com/badlogic/pi-mono/issues/157))
+
 - **HTML export line numbers**: Read tool calls in HTML exports now display line number ranges (e.g., `file.txt:10-20`) when offset/limit parameters are used, matching the TUI display format. Line numbers appear in yellow color for better visibility. ([#166](https://github.com/badlogic/pi-mono/issues/166))
 
 ### Fixed