test: add unit tests for repeatingDetector and clearCallArguments

[mason5052]

Dependency: Merge #178 first -- this PR tests the iteration cap and repeating escalation logic introduced in #178.

Description of the Change

Problem

The repeatingDetector and clearCallArguments functions in helpers.go had no unit test coverage despite being critical safety logic for preventing infinite agent chain loops (#175, #178).

Solution

Add 12 test cases covering the full behavior of repeating tool call detection:

• TestRepeatingDetector (9 cases): nil function call handling, threshold triggering at RepeatingToolCallThreshold=3, funcCalls accumulation and reset on different calls, escalation threshold validation (6 vs 7 consecutive calls), argument normalization (message field stripping, JSON key ordering)

• TestRepeatingDetectorEscalationThreshold: Validates the escalation math used in performer.go -- abort triggers when len(funcCalls) >= RepeatingToolCallThreshold + 4 = 7, confirming 4 soft warnings before abort on the 7th consecutive identical call

• TestClearCallArguments (3 cases): message field stripping, alphabetical key sorting, invalid JSON passthrough

All tests follow the existing table-driven pattern in helpers_test.go using testify/assert.

Related to #175
Adds test coverage for #178

Type of Change

• Tests (adding or updating tests)

Areas Affected

• Core Services (Backend API)

Testing and Verification

Test Configuration

• PentAGI Version: master
• Go Version: 1.24

Test Steps

1. go test ./pkg/providers/ -run "TestRepeatingDetector|TestClearCallArguments" -v -- all 12 tests pass
2. go test ./pkg/providers/ -v -- all existing tests continue to pass (no regressions)
3. go vet ./pkg/providers/ -- no warnings

Security Considerations

No security impact. Test-only change.

Checklist

• My code follows the project's coding standards
• All new and existing tests pass
• I have run go fmt and go vet
• Security implications considered
• Changes are backward compatible

[Copilot]

Pull request overview

Adds unit test coverage for the repeating tool-call detection and argument-normalization logic in backend/pkg/providers/helpers.go, which is used as safety logic to identify repeated tool calls.

Changes:

• Add table-driven tests for repeatingDetector.detect covering threshold behavior, reset behavior, and argument normalization effects.
• Add tests for repeatingDetector.clearCallArguments covering message stripping, key ordering, and invalid JSON passthrough.
• Introduce a small test helper (makeToolCall) to build llms.ToolCall inputs.

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[asdek]

tnx for the PR!