Y2B-201 — Pin and reproduce the ARMv7 build environment

> **Historical record.** The dates, candidate identity, "current" claims, > next steps and permissions below belong to this recorded boundary. See > [current state](../../CURRENT_PLATFORM_STATE.md) for the latest physically observed result.

Depends on Y2E-125/Y2E-130 (D08). Direct implementation under the owner's revised M1 model; offline only.

Deliver a checksum-locked upstream Linux v6.18 source and an isolated, version-pinned tool environment, without changing host packages, Git identity, stock loaders or the device. Keep downloads/build products ignored. Record source provenance, tool versions, deterministic build metadata and explicit preparation versus offline execution commands.

Acceptance:

Source revision and archive hash match the audited baseline; cross-check audited source hashes.
Tool environment is reconstructible from locked inputs and runs without device access; compilation uses no network.
ARMv7 compiler/linker smoke check passes and records versions; no Linux image is built yet.
Document reproducibility controls and stop conditions. Do not substitute an unpinned toolchain if preparation fails.

Validation: prepare environment, run its version inventory and compile/read an ARMv7 smoke object. This unlocks Y2B-205 (D08 validator), not device experimentation. Risk: host-only build/downloads. Return to research if upstream/tool assumptions differ.