Y2B-235 — Prove offline reproducibility and publish the launch-gated result

> **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 Y2B-230 (#14). Final small checkpoint of this offline wave; M1 hardware first boot is not yet authorized.

Acceptance:

One documented build command reconstructs all products from locked inputs, with no network/device access while compiling.
Two separate clean output directories produce identical kernel/config/DT/initramfs/BOOTIMG bytes and ELF evidence.
Full source-tree comparison against the locked archive confirms only the reviewed Kconfig overlay differs at build time.
Actual-artifact negative tests reject malformed DT/config/ELF/compressed/package evidence; final D08 report and hashes retained.
Update knowledge and milestone state with bounded offline research of U07b/U07c/U10a and backup/recovery gaps. Do not invent evidence or perform device operations.
Retain an accessible complete artifact/evidence bundle and report the conditional first-device experiment, stopping before hardware.

Validation: two clean builds match across 11 outputs; full 91,166-file/link source check passes. Nine tests pass with 20 actual-artifact corruption cases and 25 package mutation/extent cases. Final bundle is revalidated before retention. Exact reports and unresolved launch gates are in docs/build/first-boot-result.md and docs/knowledge/first-boot-launch-gates.md. M0/M1 remain open; no device command was run.