refactor: extract DeduplicateStrings helper to eliminate duplicated dedup logic

[Copilot]

The trim→skip-empty→deduplicate→optional-sort pattern was reimplemented inline in three separate packages, with behavioral drift already present (silent skip vs. error on duplicate, whitespace rejection in one but not others).

Changes

• internal/strutil/deduplicate.go — new DeduplicateStrings(input []string, sorted bool) []string canonical helper
• internal/strutil/deduplicate_test.go — table-driven tests covering nil input, trim, dedup, sort, and order preservation
• internal/difc/sink_server_ids.go — replace 14-line inline loop with strutil.DeduplicateStrings(serverIDs, true); log when entries are dropped
• internal/cmd/flags_difc.go — parseDIFCSinkServerIDs: keep the embedded-whitespace error check (not handled by the helper), delegate dedup to strutil.DeduplicateStrings
• internal/config/guard_policy.go — unchanged; normalizeAndValidateScopeArray returns an error on duplicates rather than silently dropping them, so it doesn't share the same contract

Before / After

// Before — ~15 lines repeated inline in SetSinkServerIDs
unique := make(map[string]struct{}, len(serverIDs))
normalized := make([]string, 0, len(serverIDs))
for _, serverID := range serverIDs {
    trimmed := strings.TrimSpace(serverID)
    if trimmed == "" { continue }
    if _, exists := unique[trimmed]; exists {
        duplicateIDs = append(duplicateIDs, trimmed)
        continue
    }
    unique[trimmed] = struct{}{}
    normalized = append(normalized, trimmed)
}
sort.Strings(normalized)

// After
normalized := strutil.DeduplicateStrings(serverIDs, true)

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• example.com
  • Triggering command: /tmp/go-build1731765213/b332/launcher.test /tmp/go-build1731765213/b332/launcher.test -test.testlogfile=/tmp/go-build1731765213/b332/testlog.txt -test.paniconexit0 -test.timeout=10m0s conf�� 1.4.0/auth/auth.go 1.4.0/auth/client.go x_amd64/compile (dns block)
  • Triggering command: /tmp/go-build908205860/b328/launcher.test /tmp/go-build908205860/b328/launcher.test -test.testlogfile=/tmp/go-build908205860/b328/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true --version y 06bc07c272bb18e2 ntime.v2.task/mosystemd-run containerd.sock x_amd64/vet ctl insp�� .go {{.Config.OpenSt--property=CPUQuota=5% /usr/libexec/doc--property=MemoryHigh=170M 64/src/net ache/go/1.25.8/xinfo x_amd64/vet 45045761271a86c7-collect-logs (dns block)
• invalid-host-that-does-not-exist-12345.com
  • Triggering command: /tmp/go-build1731765213/b317/config.test /tmp/go-build1731765213/b317/config.test -test.testlogfile=/tmp/go-build1731765213/b317/testlog.txt -test.paniconexit0 -test.timeout=10m0s conf�� .go (dns block)
  • Triggering command: /tmp/go-build908205860/b313/config.test /tmp/go-build908205860/b313/config.test -test.testlogfile=/tmp/go-build908205860/b313/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true 9c9123b84b4d4e8c -tests ash b8a4de3a75e76448grep fe9 x_amd64/compile fe9/init.pid --ve�� c48959766ef0f63f b8a4de3a75e764483c627dce6b038343b5b6efe353b9d178502 "CURL_CA_BUNDLE=/--systemd-cgroup b8a4de3a75e76448git (dns block)
• nonexistent.local
  • Triggering command: /tmp/go-build1731765213/b332/launcher.test /tmp/go-build1731765213/b332/launcher.test -test.testlogfile=/tmp/go-build1731765213/b332/testlog.txt -test.paniconexit0 -test.timeout=10m0s conf�� 1.4.0/auth/auth.go 1.4.0/auth/client.go x_amd64/compile (dns block)
  • Triggering command: /tmp/go-build908205860/b328/launcher.test /tmp/go-build908205860/b328/launcher.test -test.testlogfile=/tmp/go-build908205860/b328/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true --version y 06bc07c272bb18e2 ntime.v2.task/mosystemd-run containerd.sock x_amd64/vet ctl insp�� .go {{.Config.OpenSt--property=CPUQuota=5% /usr/libexec/doc--property=MemoryHigh=170M 64/src/net ache/go/1.25.8/xinfo x_amd64/vet 45045761271a86c7-collect-logs (dns block)
• slow.example.com
  • Triggering command: /tmp/go-build1731765213/b332/launcher.test /tmp/go-build1731765213/b332/launcher.test -test.testlogfile=/tmp/go-build1731765213/b332/testlog.txt -test.paniconexit0 -test.timeout=10m0s conf�� 1.4.0/auth/auth.go 1.4.0/auth/client.go x_amd64/compile (dns block)
  • Triggering command: /tmp/go-build908205860/b328/launcher.test /tmp/go-build908205860/b328/launcher.test -test.testlogfile=/tmp/go-build908205860/b328/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true --version y 06bc07c272bb18e2 ntime.v2.task/mosystemd-run containerd.sock x_amd64/vet ctl insp�� .go {{.Config.OpenSt--property=CPUQuota=5% /usr/libexec/doc--property=MemoryHigh=170M 64/src/net ache/go/1.25.8/xinfo x_amd64/vet 45045761271a86c7-collect-logs (dns block)
• this-host-does-not-exist-12345.com
  • Triggering command: /tmp/go-build1731765213/b341/mcp.test /tmp/go-build1731765213/b341/mcp.test -test.testlogfile=/tmp/go-build1731765213/b341/testlog.txt -test.paniconexit0 -test.timeout=10m0s /tmp/go-build1731765213/b271/vet.cfg flib/difflib.go main x_amd64/cgo (dns block)
  • Triggering command: /tmp/go-build908205860/b337/mcp.test /tmp/go-build908205860/b337/mcp.test -test.testlogfile=/tmp/go-build908205860/b337/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true y x_amd64/vet by/027a141771b2cb8a4de3a75e764483c627dce6b038343b5b6efe353b9d178502/log.json azero@v1.11.0/bugrep azero@v1.11.0/ca-qE x_amd64/vet 709/log.json 92b4�� by/027a141771b2cb8a4de3a75e764483c627dce6b038343b5b6efe353b9d178502 --bundle by/027a141771b2cb8a4de3a75e764483c627dce6b038343b5b6efe353b9d178502/init.pid 6efe353b9d178502bash 77a1358e1f687d17/usr/bin/runc x_amd64/vet table.d/chrony-onoffline (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

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[Copilot]

Pull request overview

This PR centralizes a common “trim → skip-empty → deduplicate → optional sort” normalization pattern into a single canonical helper to eliminate duplicated implementations and reduce behavioral drift across packages.

Changes:

• Added strutil.DeduplicateStrings helper implementing trim/skip-empty/dedup with optional sorting.
• Added table-driven tests covering trimming, empty handling, dedup behavior, order preservation, and sorting.
• Refactored DIFC sink server ID normalization and CLI flag parsing to use the shared helper.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
internal/strutil/deduplicate.go	Introduces the shared dedup/normalize helper with optional sorting.
internal/strutil/deduplicate_test.go	Adds unit tests validating helper behavior across key edge cases.
internal/difc/sink_server_ids.go	Replaces inline normalization/sort with the shared helper and logs when items are dropped.
internal/cmd/flags_difc.go	Keeps embedded-whitespace validation, delegates dedup to the shared helper.

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