fix(context_engine): prevent retry loop on connection refused errors

[tusharmath]

Summary

Improves gRPC error handling by detecting connection refused errors and preventing unnecessary retry attempts. This change eliminates retry loops when the semantic search service is offline, providing faster failure feedback and reducing system load from futile connection attempts.

Changes

Core Functionality

• Enhanced retry logic: Added connection error detection in should_retry_grpc() to identify service offline scenarios
• Error pattern matching: Checks for "Connection refused" and "tcp connect error" messages before attempting retries
• Improved logging: Updated retry warning message for better clarity

Implementation Details

• Modified should_retry_grpc() function in context_engine.rs to inspect error messages for connection failures
• Connection errors (ECONNREFUSED, tcp connect errors) now return false immediately, skipping retry logic
• Existing retry behavior preserved for transient errors (timeouts, rate limits, service unavailable without connection issues)

Testing

Added comprehensive test coverage:

• ✅ Connection refused errors (OS error 61)
• ✅ TCP connect errors
• ✅ Transport errors with connection issues
• ✅ Unavailable status with underlying connection refused (bug scenario)
• ✅ Normal unavailable errors still trigger retries (regression test)

Impact

• Faster failure detection: Applications fail immediately when service is offline instead of exhausting retry attempts
• Reduced resource usage: Eliminates CPU and network overhead from retry loops on dead connections
• Better user experience: Clearer error messages without retry noise in logs

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Co-Authored-By: ForgeCode noreply@forgecode.dev

[graphite-app]

Case-sensitive string matching will miss lowercase error messages

The string matching uses .contains("Connection refused") and .contains("tcp connect error") which are case-sensitive. If an error message contains "connection refused" (lowercase) or "TCP connect error" (uppercase), it won't be caught and will proceed to retry.

While OS errors typically use consistent casing, different OS versions, libraries, or error wrapping could produce varied casing.

Fix:

let error_msg = format!("{:#}", error).to_lowercase();
if error_msg.contains("connection refused") || error_msg.contains("tcp connect error") {
    return false;
}

Suggested change

	let error_msg = format!("{:#}", error);
	if error_msg.contains("Connection refused") || error_msg.contains("tcp connect error") {
	return false;
	let error_msg = format!("{:#}", error).to_lowercase();
	if error_msg.contains("connection refused") || error_msg.contains("tcp connect error") {
	return false;

Spotted by Graphite Agent



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