docs(buck2): record blocked NativeLink RE probe

[schickling-assistant]

Problem

Buck actions are currently local-only even when an REAPI endpoint is configured, so the NativeLink replacement question needs action-level execution evidence rather than cache-only evidence.

Goal

Preserve the exact dev4 probe, its opt-in graph patch, and the blocked result without changing production defaults or claiming an execution result.

Decisions

None. This is evidence only. The fixture uses localhost plaintext gRPC, an isolated instance name, and a separate remote-only aarch64 platform.

Verification

• git apply --check context/buck2/.experiments/2026-09-19-nativelink-remote-execution/remote-execution.patch
• bash -n context/buck2/.experiments/2026-09-19-nativelink-remote-execution/run-dev4.sh
• git diff --cached --check before commit
• axe vrs check --profile strict context/buck2 reports no error for the new experiment; it remains red on unchanged decision records 0035 and 0036.
• On dev4, NativeLink 1.7.1 failed while building compiler-rt 22.1.8 (sys/auxv.h missing). The pinned 1.6.6 retry was stopped before startup when shared-host disk/memory pressure crossed the recorded safety boundary.

No NativeLink process started and no Buck action ran, so remote execution and cache behavior remain unproven.

Complexity

Five evidence files, all under context/buck2/.experiments: one record, one NativeLink config, one Buck config, one generated opt-in patch, and one teardown-safe runner. No production source file changes.

Concerns

The config is a localhost proof fixture, not a secure deployment topology. Cross-host workers would also need the exact /nix/store closure available outside REAPI inputs.

Friction & bottlenecks

The current NativeLink flake does not realize on aarch64 dev4, and the older pin's uncached closure exceeded the safe envelope while unrelated CI was active.

Follow-ups

A future rerun requires a substituted/packageable aarch64 NativeLink binary and an adequate host-capacity window. This record makes no infrastructure decision.

References

• https://buck2.build/docs/users/remote_execution/
• https://buck2.build/docs/api/build/CommandExecutorConfig/
• https://github.com/TraceMachina/nativelink/blob/a21edb0fc56879124e308bb9a67be679f8eaf885/nativelink-config/examples/local_rbe_self_test.json5

Posted on behalf of @schickling

field	value
agent_identity	dev3.direct.omp.t3mkm4sd
session	unknown
agent_persona	generalist
agent_supervisor	unavailable
agent_tool	OMP
agent_tool_version	18.1.14
agent_runtime	OMP 18.1.14
tooling_profile	dotfiles@5d1e05f

[schickling-assistant]

Superseded: this record landed on main via #1319 (experiments) / #1301 (key-stability evidence, DELTA-001 removal). Closing per the 2026-09-22 stack handoff.