[test] Add tests for server.ensureGuardInitialized and normalizeScopeKind

[github-actions]

Test Coverage Improvement: ensureGuardInitialized + normalizeScopeKind

Functions Analyzed

	Detail
Package	internal/server
File	unified.go
Functions	ensureGuardInitialized (~100 LOC, high complexity) + normalizeScopeKind
Previous Coverage	0% direct coverage (only indirect via integration-style callBackendTool tests)
New Coverage	All branches covered
Complexity	High – ensureGuardInitialized has 10+ distinct branches including caching, error propagation, session creation, label merging, and mode parsing

Why These Functions?

ensureGuardInitialized is the core DIFC session-initialization routine. It:

• Resolves and validates the guard policy
• Implements a policy-hash-keyed cache to avoid redundant LabelAgent calls
• Parses DIFCMode strings from guard results
• Merges secrecy/integrity tags into the agent registry
• Creates session state on first use

Despite being central to DIFC enforcement, it had zero direct test coverage – every branch was reachable only via expensive end-to-end callBackendTool integration tests that require a live HTTP backend.

normalizeScopeKind is a pure helper with no tests at all.

Tests Added

normalizeScopeKind (7 tests):

• ✅ nil input → nil output
• ✅ Empty map → empty map copy
• ✅ Map without scope_kind field → copy unchanged
• ✅ scope_kind already lowercase → unchanged
• ✅ scope_kind UPPERCASE → lowercased
• ✅ scope_kind mixed-case + whitespace → trimmed and lowercased
• ✅ Non-string scope_kind → type assertion skipped, value preserved
• ✅ Input map not mutated (returns copy)

ensureGuardInitialized (12 tests):

• ✅ Policy nil → evaluator default mode returned, no error
• ✅ resolveGuardPolicy error → wrapped error propagated
• ✅ Cache hit (same session/server/policy hash) → LabelAgent not called again
• ✅ LabelAgent returns error → error propagated
• ✅ LabelAgent returns nil result → error propagated
• ✅ DIFCMode empty → falls back to evaluator default
• ✅ DIFCMode valid non-empty → overrides evaluator default
• ✅ DIFCMode invalid string → error propagated
• ✅ New session created when none exists; GuardInit state written correctly
• ✅ Labels from LabelAgent merged into agentRegistry
• ✅ Stale policy hash → cache invalidated, LabelAgent re-called
• ✅ Existing session with nil GuardInit map → map created before writing
• ✅ Normalized policy stored with scope_kind lowercased via normalizeScopeKind
• ✅ Multiple serverIDs tracked independently within the same session
• ✅ Union-semantics: tags from multiple guards are additive, not overwriting

Implementation Notes

Tests use a lightweight newMinimalUnifiedServer helper that constructs a UnifiedServer directly (without calling NewUnified or starting backend servers), making them fast pure-unit tests with no network or process dependencies.

Three new test doubles are introduced:

• configurableGuard – configurable LabelAgent return values per test
• countGuard – wraps configurableGuard to count LabelAgent invocations
• noopBackendCaller – no-op guard.BackendCaller

All names are distinct from existing test types in the package (mockGuard, writeSinkTestGuard, labelAgentTestGuard).

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Generated by Test Coverage Improver
Next run candidates: resolveGuardPolicy Guards-config path, mcp.initializeHTTPSession error branches, config.validateStandardServerConfig HTTP+mounts path

Generated by Test Coverage Improver · ◷

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[Copilot]

Pull request overview

Adds direct unit tests in internal/server to cover DIFC session initialization behavior and a small policy normalization helper, improving coverage of high-branch logic in UnifiedServer.ensureGuardInitialized and normalizeScopeKind without relying on integration-style tests.

Changes:

• Introduces focused unit tests for normalizeScopeKind covering nil/empty inputs, casing/whitespace normalization, type preservation, and non-mutation behavior.
• Adds unit tests for ensureGuardInitialized covering policy resolution errors, cache-hit behavior, label_agent error/edge cases, DIFCMode parsing/fallback, session state creation, normalized policy persistence, and union semantics for label merging.

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