feat(lab): mike_upstream_native_v1 - full pinned upstream surface arm

One flag (MIKE_UPSTREAM_NATIVE=1) selects the 2266446b project-chat
surface end to end: pinned system prompt (Phase-1 strip-list, hashes in
the surface file), the nine-tool native array in upstream order, the
native AVAILABLE DOCUMENTS block with read-once trailer, native
tool-result envelopes (citationReminder prefix, find {index,excerpt,
context} hits, native already_read payload), maxIterations=10 from the
chat.ts call site, and native ask_inputs turn termination recorded as a
typed receipt (ask_inputs_terminated) instead of being suppressed.

upstreamNativeDocxRenderer.ts ports the pinned sections[]->OOXML
renderer (2266446b documentOps.ts:83-582) and the pinned DOCX read
plane, so read_document, find_in_document, and edit_document all serve
the same characters upstream serves (including upstream's numeric w:t
coercion defect - the arm measures what an upstream user receives).
Native edit_document applies partial-success tracked edits as author
"Mike" and clears the read guard for post-edit verification reads.

Conformance: prompt-sha gate plus a full isolation predicate for the
arm; before/after tool-selection sweep identical across all 14 arms
(zero drift with the flag off); tsc clean at 0 errors.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011pfUVhNFTRvhYGXBwoKNj6