refactor: consolidate duplicate DIFC filtered-item struct and tagsToStrings

[Copilot]

Two duplication patterns introduced in internal/server/difc_log.go required parallel edits across files when modifying DIFC filter event data shapes.

Changes

• Struct consolidation — FilteredItemLogEntry (server) and JSONLFilteredItem (logger) shared identical 11-field data definitions. Moved the shared fields into a new logger.FilteredItemLogEntry; JSONLFilteredItem now embeds it, keeping only its own Timestamp and Type fields:

  // Before: 11 fields duplicated verbatim in both structs
  type JSONLFilteredItem struct {
      Timestamp string `json:"timestamp"`
      Type      string `json:"type"`
      ServerID  string `json:"server_id"`
      // ... 9 more duplicated fields
  }
  
  // After: embed the shared struct
  type JSONLFilteredItem struct {
      Timestamp string `json:"timestamp"`
      Type      string `json:"type"`
      FilteredItemLogEntry
  }

• Remove toJSONLFilteredItem() — field-by-field copy method replaced with a direct struct literal: &logger.JSONLFilteredItem{FilteredItemLogEntry: entry}

• Eliminate duplicate tagsToStrings — local helper in difc_log.go was identical to difc.TagsToStrings; replaced all call sites with the canonical package function

• Test updates — difc_log_test.go updated to reference logger.FilteredItemLogEntry instead of the removed local type

Warning

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• example.com
  • Triggering command: /tmp/go-build3728142662/b332/launcher.test /tmp/go-build3728142662/b332/launcher.test -test.testlogfile=/tmp/go-build3728142662/b332/testlog.txt -test.paniconexit0 -test.timeout=10m0s rev-�� /unix (dns block)
• invalid-host-that-does-not-exist-12345.com
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• slow.example.com
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• this-host-does-not-exist-12345.com
  • Triggering command: /tmp/go-build3728142662/b341/mcp.test /tmp/go-build3728142662/b341/mcp.test -test.testlogfile=/tmp/go-build3728142662/b341/testlog.txt -test.paniconexit0 -test.timeout=10m0s rev-�� ache/go/1.25.8/x64/src/runtime/cgo1.25.8 (dns block)

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[Copilot]

Pull request overview

This PR reduces duplication in DIFC filtered-item logging by centralizing the shared filtered-item payload fields in the internal/logger package and reusing existing DIFC tag conversion helpers, so future schema changes require fewer parallel edits.

Changes:

• Consolidates the shared filtered-item payload into logger.FilteredItemLogEntry and embeds it into logger.JSONLFilteredItem.
• Simplifies DIFC JSONL emission by removing the per-field conversion helper and using a direct struct literal.
• Replaces the duplicated tagsToStrings helper in difc_log.go with difc.TagsToStrings, and updates tests accordingly.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
internal/server/difc_log.go	Switches filtered-item entry construction to logger.FilteredItemLogEntry, uses difc.TagsToStrings, and simplifies JSONL logging construction.
internal/logger/jsonl_logger.go	Introduces FilteredItemLogEntry and embeds it into JSONLFilteredItem to eliminate duplicated field definitions.
internal/server/difc_log_test.go	Updates tests to unmarshal/compare against logger.FilteredItemLogEntry.

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