Preserve actionable initialize errors after CLI process exit

[shuofengzhang]

What changed

• Capture result messages with subtype="error_during_execution" in Query._read_messages and store the CLI-provided error text.
• When the reader later exits with a ProcessError, propagate the captured CLI error text to pending control requests (such as initialize) instead of the generic process-exit placeholder.
• Add a regression test (TestInitializeErrorPropagation) that reproduces the failure mode and verifies the propagated exception contains the real CLI error text.

Why

• In the failing initialize path, the CLI can emit an error_during_execution result on the message stream and then exit non-zero.
• Previously, the non-zero exit became a generic ProcessError ("Check stderr output for details") that overwrote pending control requests, so callers waiting on initialize() lost the actionable root-cause message.

Insight / Why this matters

The core issue is a cross-channel ordering bug:

1. The real failure reason is emitted as a result message (error_during_execution) on the message stream.
2. initialize() is waiting on the control-response channel, not message iteration.
3. Process exit then raises ProcessError, and that generic error replaced the pending control result.

This is easy to miss because both error signals exist, but only one is observed by initialize callers. Preserving the CLI-emitted execution error keeps diagnostics aligned with actual root cause.

Practical gain / Why this matters

• Callers now receive actionable initialize failures (for example, invalid/missing session IDs) instead of a generic stderr hint.
• Improves reliability of error handling in SDK integrations and reduces debugging/triage time when startup fails.

Testing

• ✅ pytest -q tests/test_query.py -k "initialize_uses_error_during_execution_result_text"
• ✅ pytest -q

Risk analysis

• Scope is intentionally narrow: only affects how pending control waiters are failed when a ProcessError follows a known error_during_execution result.
• No protocol or transport shape changes.
• Regression test covers the exact failure ordering to protect against future regressions.