Clone shared runOptions before appending per-run options

[PratikDhanave]

In prepareRun, the agent-configured run options were prepended with:

if len(a.runOptions) != 0 {
    options = append(a.runOptions, options...)
}

a.runOptions is a field shared across every run of the Agent, and New builds it with slices.Clone(cfg.RunOptions) followed by a per-tool append(..., WithTool(tool)), which routinely leaves the slice with spare capacity. Because of that spare capacity, append(a.runOptions, options...) writes each run’s per-run options — the synthesized WithSession(...)/noSessionProvided(true), or a caller’s WithServiceID — into a.runOptions[len:cap], memory shared across all runs.

When a single *Agent (with ≥1 configured tool, the normal case) serves concurrent runs — the natural usage for an agent framework — this is a data race, and one run can observe another run’s clobbered session/service ID reaching the provider. Sequential runs mask it because length-bounded reads never see runOptions[len:].

Every other analogous spot in the package already clones before appending a shared slice (New clones RunOptions, Middlewares, prov.Middlewares; invoke clones options); this prepend site missed it.

Fix

options = append(slices.Clone(a.runOptions), options...)

Test

TestAgent_ConcurrentRunsDoNotShareRunOptions builds an agent with tools (so runOptions has spare capacity) and issues 64 concurrent runs, each with its own WithServiceID/WithSession. Under -race it reports a DATA RACE in prepareRun on the old code and passes with the fix.

[Copilot]

Pull request overview

This pull request fixes a concurrency/data-race bug where per-run options could be appended into the Agent’s shared runOptions backing array due to spare slice capacity, causing cross-run option corruption under concurrent runs.

Changes:

• Clone a.runOptions in prepareRun before prepending run-scoped options to avoid mutating shared backing storage.
• Add a regression test that runs many concurrent agent runs (with configured tools to ensure spare capacity) and relies on -race to detect the prior data race.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
agent/agent.go	Clones shared runOptions before append to prevent concurrent mutation of the shared slice backing array.
agent/agent_test.go	Adds a -race regression test covering concurrent runs to ensure options aren’t shared/mutated across runs.

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[github-actions]

Parity Review: No Issues Found

This PR fixes an internal data race in prepareRun by cloning a.runOptions before appending per-run options (slices.Clone(a.runOptions)). No exported Go types, methods, functions, or observable user-facing behaviors are changed.

Scope: Internal unexported logic only — prepareRun, a.runOptions (unexported field), and concurrency safety of per-run option merging.

Cross-repo parity: Not applicable. This is a Go-internal concurrency correctness fix with no equivalent API surface in the upstream .NET or Python implementations to compare against.

Label actions: parity-approved label correctly remains; public-api-change label is not warranted.

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