refactor: address semantic function clustering outliers — doc comments, rename, dead code removal

[Copilot]

Implements the Priority 1 and Priority 2 recommendations from the semantic function clustering analysis: one explanatory comment gap, one misleading filename, and one dead private wrapper.

Changes

• internal/config/expand.go — Added package-level doc comment explaining why this file uses os.LookupEnv directly instead of internal/envutil. The distinction is semantic: envutil silently returns defaults for undefined vars; config expansion must fail hard on undefined references.

  // Why this file does NOT reuse internal/envutil:
  //
  // internal/envutil is a generic, low-level toolkit (GetEnvString, GetEnvIntRaw, …)
  // that returns defaults or zero values when a variable is undefined.  Config
  // expansion has stricter semantics: an undefined variable referenced in a
  // configuration file is a hard error, not a silent fallback.

• internal/config/config_env.go → internal/config/gateway_env.go — Renamed via git mv to accurately reflect the file's scope (gateway-specific env accessors), distinguishing it from expand.go which handles ${VAR} substitution.

• internal/logger/rpc_format.go — Removed the dead truncateAndSanitize private wrapper and its unused sanitize/util imports. The function had no production call sites; rpc_logger.go already calls sanitize.SanitizeString and util.Truncate directly (and more efficiently, reusing the sanitized string across multiple truncation lengths). Removed the corresponding TestTruncateAndSanitize test.

• internal/logger/global_state.go — No change; the cross-referencing "Log-Level Quad-Function Pattern" comment documenting the three logWith* dispatchers already exists.

[Copilot]

Pull request overview

Refines configuration and logger organization following semantic clustering analysis.

Changes:

• Documents strict configuration environment expansion semantics.
• Renames gateway environment helpers for clarity.
• Removes an unused sanitization wrapper and its tests.

Show a summary per file

File	Description
internal/config/expand.go	Documents strict undefined-variable handling.
internal/config/gateway_env.go	Renames gateway-specific environment helpers.
internal/logger/rpc_format.go	Removes the dead wrapper and imports.
internal/logger/rpc_helpers_test.go	Removes obsolete wrapper tests.

Review details

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Comments suppressed due to low confidence (1)

internal/config/gateway_env.go:3

• The rename leaves the project-structure guide at AGENTS.md:31 pointing to the now-nonexistent config_env.go. Update that entry to gateway_env.go so contributor documentation remains accurate.

• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Medium