tracing: fix StartProxyForwardSpan dead code by adding serverAddress param

[Copilot]

StartProxyForwardSpan in internal/tracing/span_helpers.go was dead code — it omitted semconv.ServerAddressKey, causing internal/proxy/handler.go to inline the span creation with a diverged attribute set instead of using the helper.

Changes

• internal/tracing/span_helpers.go — Add serverAddress string parameter to StartProxyForwardSpan; include semconv.ServerAddressKey in span attributes to match the live inline version
• internal/proxy/handler.go — Replace inline "proxy.backend.forward" span creation with tracing.StartProxyForwardSpan; remove now-unused oteltrace import
• internal/tracing/span_helpers_test.go — Update call site and add assertion for semconv.ServerAddressKey

// Before: inline in handler.go
fwdCtx, fwdSpan := h.GetTracer().Start(ctx, "proxy.backend.forward",
    oteltrace.WithAttributes(
        semconv.URLPathKey.String(r.URL.Path),
        semconv.ServerAddressKey.String(h.server.upstreamHost()),
        tracing.GenAIToolName.String(toolName),
    ),
    oteltrace.WithSpanKind(oteltrace.SpanKindClient),
)

// After: via helper
fwdCtx, fwdSpan := tracing.StartProxyForwardSpan(ctx, h.GetTracer(), toolName, r.URL.Path, h.server.upstreamHost())

[lpcox]

@copilot resolve the merge conflicts in this pull request

[Copilot]

Pull request overview

This PR standardizes OpenTelemetry span creation for proxied backend forwarding by fixing the StartProxyForwardSpan helper to include the server.address attribute, then reusing the helper from the proxy handler to avoid duplicated/diverged span attribute sets.

Changes:

• Extend tracing.StartProxyForwardSpan to accept serverAddress and set semconv.ServerAddressKey.
• Replace the inline "proxy.backend.forward" span creation in the proxy handler with the tracing helper (and remove the now-unused otel/trace import).
• Update tracing helper tests to pass a server address and assert the server.address attribute is recorded.

Show a summary per file

File	Description
internal/tracing/span_helpers.go	Adds serverAddress parameter and includes semconv.ServerAddressKey on the forward span.
internal/proxy/handler.go	Switches forward-span creation to tracing.StartProxyForwardSpan and drops the unused oteltrace import.
internal/tracing/span_helpers_test.go	Updates the helper call and asserts the new server.address span attribute.

Copilot's findings

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• Files reviewed: 3/3 changed files
• Comments generated: 0

[Copilot]

@copilot resolve the merge conflicts in this pull request

Conflicts are resolved in commit 016d132e by merging origin/main into this branch and resolving the internal/tracing/span_helpers.go conflict while preserving the server.address span attribute.