fix(rmcp-client): label phase errors, retry transient init (#378)

[zemaj]

Summary

• add explicit phase context to initialize/list/call MCP failures so logs show where the request died
• retry the Streamable HTTP initialize handshake once on obvious transient network errors before surfacing failure
• cover the new helpers with unit tests for phase labeling and retry gating

Testing

• cargo test -p code-rmcp-client
• ./build-fast.sh

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Propagate original handshake error so retries can detect transients

The new retry path in initialize relies on should_retry_initialize walking the error chain for ReqwestError or io::Error, but handshake_failed_error recreates the error with anyhow!(...) and drops the original source. After this wrapper runs the chain only contains the formatted string, so should_retry_initialize will never see the underlying transport error and the streamable HTTP initialize handshake will never be retried. Consider wrapping the incoming error instead of formatting it (e.g. err.context(...)) so its type survives downcasting.

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[zemaj]

Summary:

• Added bounded exponential retries (max 3, 200 ms base, cap 1.6 s) when the streamable HTTP handshake flakes.
• Treated handshake timeouts and common IO reset errors as transient so we rebuild the transport before retrying.
• Extended unit coverage for phase annotation, retry gating, and backoff math.

Tests:

• cargo test -p code-rmcp-client --tests
• ./build-fast.sh

Risks:

• Backoff remains deterministic; consider jitter if servers see herd retries.