[log] log: add debug logging to proxy/graphql_rewrite.go

[github-actions]

Summary

Adds debug logging to internal/proxy/graphql_rewrite.go using the existing logGraphQL logger (defined in graphql.go, same package). No new logger declaration is needed.

Changes

File modified: internal/proxy/graphql_rewrite.go (1 file, exactly)

Logging added

InjectGuardFields — entry + all early-return paths:

• Entry log: toolName and bodyLen for traceability
• Fields-not-needed path: logs when no guard fields apply to the tool
• Unmarshal error path: logs parse failure with tool name and error
• All-present / empty-query path: logs skip with reason
• No-change path: logs when injection produced no diff (no-op)

injectFieldsIntoQuery — injection strategy chosen:

• Fragment path: logs fragName and injected fields
• Direct nodes path: logs fields being injected inline
• No-match path: logs when no injection point was found

Before

InjectGuardFields had a single log call only on the success-injection path. Silent failures (parse errors, no-op injections, wrong tool name) were invisible in debug output.

After

Every significant control-flow branch emits a debug log, making it straightforward to trace why a guard-field injection did or did not happen for a given request.

Quality checklist

• Exactly 1 file modified
• No test files modified
• Reuses existing logGraphQL logger (no duplicate declaration)
• Logger naming follows pkg:filename convention (proxy:graphql)
• Log arguments are pure variable references — no side effects
• Messages are meaningful and useful for debugging
• No duplication with existing log call (the success-injection log is preserved as-is)
• Import statements unchanged (no new imports needed)

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