docs(agent-governance): add Grok 4.3 / Grok Build engineering harness (#798)
* feat: add Grok 4.3 agent config, GROK.md, GPT55.md, handoff template, and .env additions
- GROK.md: full agent instructions optimized for Grok 4.3 high-effort mode
- GPT55.md: agent instructions for GPT-5.5 (o3-level reasoning, stateless)
- docs/handoff_template.md: mandatory cross-session handoff artifact template
- .env.grok43: Grok 4.3 environment config additions (do not commit secrets)
- AGENTS.md: prepend Grok 4.3 multi-agent/Arena mode addendum block
* feat: prepend Grok 4.3 / GPT-5.5 multi-agent addendum to AGENTS.md
* refine GROK.md: add Versor Coherence Guardian Protocol section + tighten NON-NEGOTIABLE INVARIANTS with explicit versor_apply / cga_inner / FieldState / claim schema / safety pack rules for stronger algebraic and epistemic guardrails
* refine AGENTS.md: align Grok 4.3 / Grok Build hard stops with refined GROK.md (Plan Mode, skills system, Versor Coherence Guardian references) while preserving full compatibility for Claude
* upgrade docs/handoff_template.md to mastery level for Grok Build: add Versor Coherence Guardian checks, subagent reconciliation section, skills usage tracking, and stronger invariant verification language
* expand .env.grok43 into full Grok Build mastery configuration (skills dir, Plan Mode preference, Arena settings, auto-invoke)
* create skills/core-bootstrap.md - highest priority Grok Build skill for statelessness compensation
* create skills/versor-coherence-guardian.md - critical Grok Build skill enforcing the new Versor Coherence Guardian Protocol
* create skills/pre-edit-sweep.md - Grok Build skill implementing the Pre-Edit Sweep Protocol at mastery level
* create skills/claim-proposal-guardian.md - Grok Build skill protecting claim schema and epistemic rigor
* create docs/core-rd-base-prompts.md - high-signal, architecture-grounded prompt library for HITL and agentic use (lightly polished for structure and scannability)
* add Phase-Specific Prompt Library reference section to GROK.md pointing to the new docs/core-rd-base-prompts.md
* add reference to docs/core-rd-base-prompts.md in AGENTS.md Grok section
* add prompt library reference to handoff_template.md in the 'What Must Not Be Forgotten' section
* move .env.grok43 to docs/examples/grok43.env.example as a proper example file
* remove old .env.grok43 (moved to docs/examples/grok43.env.example)
* update docs/core-rd-base-prompts.md: fix epistemic wording + add sections #8 PR Merge-Readiness Audit and #9 Grok Build Implementation Session
* make 'full suite before merge' rule scope-sensitive in GROK.md for docs/config-only changes
* add reference to new prompt sections #8 and #9 in handoff_template.md
* create docs/grokbuild/README.md - comprehensive SpaceX-level mastery guide for using Grok 4.3 + Grok Build on CORE
* fix broken markdown fences in sections #8 and #9 of docs/core-rd-base-prompts.md
* fix skill invocation wording and soften curl|bash recommendation in docs/grokbuild/README.md
* docs(agent-governance): clean handoff template whitespace
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