InMemoryBackend: deep-copy values on Set/Get to fix data race

[AbirAbbas]

Summary

• Recursive deepCopyAny for map[string]any, []any, and []float64 applied on Set, Get, SetVector, GetVector
• Callers and the backend never share mutable references, preventing data races
• Verified with go vet clean and go test -race ./agent/

Changes

• agent/backend/inmemory/inmemory.go — Added deepCopyAny helper and applied it to Set, Get, SetVector, GetVector
• agent/backend/inmemory/inmemory_test.go — Added regression tests that mutate originals and returned values, asserting stored state is unchanged; concurrent access test

Test plan

1. Run go vet ./agent/... — passes clean
2. Run go test -race ./agent/... — all tests pass with race detector enabled
3. Regression tests verify that mutating returned values does not affect stored state and vice versa
4. Concurrent access test verifies no data races under parallel reads/writes

Closes #432

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[github-actions]

Performance

SDK	Memory	Δ	Latency	Δ	Tests	Status
Go	190 B	-32%	0.47 µs	-53%	✓	✓

✓ No regressions detected

[github-actions]

📊 Coverage gate

Thresholds from .coverage-gate.toml: per-surface ≥ 84%, aggregate ≥ 85%, max per-surface regression ≤ 1.0 pp, max aggregate regression ≤ 0.50 pp.

Surface	Current	Baseline	Δ
control-plane	86.90%	87.40%	↓ -0.50 pp	🟡
sdk-go	92.50%	92.00%	↑ +0.50 pp	🟢
sdk-python	93.82%	93.73%	↑ +0.09 pp	🟢
sdk-typescript	91.05%	90.42%	↑ +0.63 pp	🟢
web-ui	84.75%	84.79%	↓ -0.04 pp	🟡
aggregate	85.54%	85.75%	↓ -0.21 pp	🟡

✅ Gate passed

No surface regressed past the allowed threshold and the aggregate stayed above the floor.

[github-actions]

📐 Patch coverage gate

Threshold: 80% on lines this PR touches vs origin/main (from .coverage-gate.toml:thresholds.min_patch).

Surface	Touched lines	Patch coverage	Status
control-plane	0	—	➖ no changes
sdk-go	35	100.00%	✅
sdk-python	0	—	➖ no changes
sdk-typescript	0	—	➖ no changes
web-ui	0	—	➖ no changes

✅ Patch gate passed

Every surface whose lines were touched by this PR has patch coverage at or above the threshold.

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