Refactor internal helper placement and naming to resolve semantic clustering outliers

[Copilot]

This PR resolves the semantic clustering findings across internal/ by relocating outlier functions/types to their owning domains and removing duplicate validation logic between config and guard. It also resolves an ambiguous transport-vs-server session method name collision.

• Config expansion logic consolidation

  • Moved expandMapInPlace and expandTracingVariables into internal/config/expand.go so ${VAR} expansion behavior lives in one place.
  • Removed duplicated definitions from config_stdin.go and config_tracing.go.

• Guard/config validator consolidation

  • Added canonical reusable validators in internal/config/guard_policy_validation.go:
    • ValidateStringArrayField
    • IsValidAllowOnlyReposValue
  • Updated internal/guard/wasm_validate.go to delegate to config validators instead of reimplementing equivalent checks.

• WASM guard discovery ownership moved to guard

  • Moved filesystem discovery helpers into internal/guard/wasm.go:
    • GetWASMGuardsRootDir
    • FindServerWASMGuardFile
  • Updated internal/server/guard_init.go and related tests to call guard-owned helpers.

• DIFC filtered-item map helper outliers removed

  • Inlined author/number extraction directly in buildFilteredItemLogEntry (internal/server/difc_log.go) per issue recommendation.
  • Removed standalone helper test file and added focused edge-case coverage in difc_log_test.go.

• Logger cleanup API scope

  • Unexported ExtractErrorMessage to extractErrorMessage (internal/logger/log_cleanup.go) since usage is internal/test-only.

• MCP tag snapshot type placement

  • Moved AgentTagsSnapshot and GetAgentTagsSnapshotFromContext from connection.go to connection_logging.go to colocate declarations with actual logging consumers.

• Label-agent helper placement

  • Moved emptyAgentLabelsResult and ApplyLabelAgentResult from internal/guard/guard.go to internal/guard/label_agent.go alongside RunLabelAgent.

• Session ID truncation ownership

  • Moved session-specific truncation behavior from internal/strutil into internal/server/session_util.go as truncateSessionID.
  • Updated server call sites; removed TruncateSessionID from strutil and moved tests to server package.

• Naming collision removal

  • Renamed (*mcp.Connection).requireSession() to requireSDKSession() to distinguish SDK transport session validation from server.requireSession(ctx) lifecycle behavior.

// before
if err := c.requireSession(); err != nil { ... }

// after
if err := c.requireSDKSession(); err != nil { ... }

[Copilot]

Pull request overview

This PR refactors several internal helpers to better align them with their owning domains (server/guard/config/logger/mcp), reduces duplicated validation logic, and resolves a session-method naming collision in the MCP connection layer.

Changes:

• Moved session-ID truncation logic from internal/strutil into internal/server and updated all server logging call sites and tests.
• Moved WASM guard discovery helpers into internal/guard and updated server initialization/tests to use guard-owned discovery.
• Consolidated duplicated validation and expansion helpers (config/guard), simplified DIFC filtered-item metadata extraction, and renamed MCP SDK session validation helper to requireSDKSession.

Show a summary per file

File	Description
internal/strutil/truncate.go	Removes server-specific TruncateSessionID from shared string utilities.
internal/strutil/truncate_test.go	Removes TruncateSessionID tests now that behavior is owned by server.
internal/server/unified_wasm_guards_dir_test.go	Updates WASM guard discovery tests to exercise guard.FindServerWASMGuardFile.
internal/server/session.go	Switches session logging to use truncateSessionID in server package.
internal/server/session_util.go	Adds server-owned truncateSessionID helper for safe session logging.
internal/server/session_util_test.go	Adds focused unit tests for server-owned session truncation.
internal/server/session_auto_init.go	Updates auto-init logging to use server-owned session truncation.
internal/server/routed.go	Updates cache/log output to use server-owned session truncation.
internal/server/middleware.go	Updates OTEL/logging code paths to use server-owned session truncation.
internal/server/http_helpers.go	Updates request-body logging to use server-owned session truncation.
internal/server/guard_init.go	Delegates per-server WASM guard discovery/root-dir lookup to internal/guard.
internal/server/difc_log.go	Inlines author/number extraction into buildFilteredItemLogEntry and removes helpers.
internal/server/difc_log_test.go	Adds edge-case coverage for author-login and number extraction in the inlined logic.
internal/server/difc_log_helpers_test.go	Removes tests for helper functions that were deleted.
internal/mcp/sdk_method_dispatch_test.go	Updates comments to reflect requireSDKSession rename.
internal/mcp/pagination.go	Renames SDK session validation calls to requireSDKSession.
internal/mcp/pagination_test.go	Updates test comments to match requireSDKSession rename.
internal/mcp/connection.go	Renames requireSession to requireSDKSession and moves tag snapshot type out to logging file.
internal/mcp/connection_test.go	Updates tests to call requireSDKSession.
internal/mcp/connection_logging.go	Relocates AgentTagsSnapshot + context extraction helper alongside logging consumers.
internal/logger/rpc_helpers_test.go	Updates tests/benchmarks to call unexported extractErrorMessage.
internal/logger/log_cleanup.go	Unexports ExtractErrorMessage to extractErrorMessage.
internal/guard/wasm.go	Adds guard-owned WASM discovery helpers (GetWASMGuardsRootDir, FindServerWASMGuardFile).
internal/guard/wasm_validate.go	Delegates string-array and allow-only repo validation to canonical config validators.
internal/guard/label_agent.go	Moves label-agent helper functions into label-agent file alongside RunLabelAgent.
internal/guard/guard.go	Removes label-agent helpers now relocated to label_agent.go.
internal/config/guard_policy_validation.go	Adds canonical reusable validators (ValidateStringArrayField, IsValidAllowOnlyReposValue).
internal/config/expand.go	Centralizes expandMapInPlace and expandTracingVariables into a shared expansion module.
internal/config/config_tracing.go	Removes duplicated tracing-variable expansion helper.
internal/config/config_stdin.go	Removes duplicated map expansion helper; continues calling shared helper.

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• Files reviewed: 30/30 changed files
• Comments generated: 0