[test] Add tests for server.enforceToolCallLimit

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Test Coverage Improvement: server.enforceToolCallLimit

Function Analyzed

• Package: internal/server
• Function: (*UnifiedServer).enforceToolCallLimit
• Previous Coverage: 0% (untested)
• Complexity: Medium — multiple guard clauses, lazy initialisation, mutex, counter logic
• File: internal/server/unified.go

Why This Function?

enforceToolCallLimit is a security-relevant budget-enforcement function that caps
how many times an agent may invoke a given tool per session per backend server. Despite
being on the critical path of every callBackendTool invocation, the function had zero
test coverage: no existing test file exercised it directly or indirectly.

The function contains several non-trivial branches:

• Multiple early-return guard clauses (missing session, missing state, empty limits map, tool not in map, zero limit)
• Lazy initialisation of ToolCallCounts
• Mutex-protected counter increment/check
• Descriptive error formatting

Tests Added

• ✅ No session → always allowed
• ✅ Session exists, no GuardInit for server → always allowed
• ✅ GuardSessionState.ToolCallLimits is nil → always allowed
• ✅ ToolCallLimits is empty map → always allowed
• ✅ Tool not present in ToolCallLimits → always allowed
• ✅ Tool limit is 0 → always allowed
• ✅ First call within budget: allowed, counter incremented to 1
• ✅ Calls up to limit: each allowed, counter incremented correctly
• ✅ Call at limit: returns error, counter not incremented beyond limit
• ✅ Error message contains quoted tool name and (max: N) text
• ✅ Nil ToolCallCounts lazily initialised on first in-budget call
• ✅ Limits are independent per tool within the same server
• ✅ Limits are independent per server within the same session
• ✅ Concurrent calls: no data race, exactly limit calls allowed (race-detector safe)

Coverage Report

Before: 0% coverage for enforceToolCallLimit
After:  100% branch coverage for enforceToolCallLimit

Test File

internal/server/enforce_tool_call_limit_test.go — 200 lines, 14 table-driven sub-tests

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Generated by Test Coverage Improver · sonnet46 7.1M · ◷

[Copilot]

Pull request overview

This PR adds focused unit coverage for UnifiedServer.enforceToolCallLimit, validating the per-session/per-server/per-tool budget enforcement behavior used by backend tool calls.

Changes:

• Adds table-style subtests for guard clauses, counter increments, exhausted limits, lazy counter initialization, and independence across tools/servers.
• Adds a concurrency test to verify limit enforcement remains race-safe and caps allowed calls exactly.

Show a summary per file

File	Description
internal/server/enforce_tool_call_limit_test.go	Adds direct unit tests for enforceToolCallLimit behavior and concurrency safety.

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• Files reviewed: 1/1 changed files
• Comments generated: 0