docs(CH-012): clarify Rumble runtime distributions

[flemming-n-larsen]

Acceptance brief

• Plan item and whether it remains wanted: P-003/M-008 remains wanted.
• Added or changed criteria and advisory verdicts: RCL-008 is retired because it coupled runtime portability to an ambiguous all-in-one container boundary (undetermined, superseded); RCL-010 defines supported native and Docker multi-runtime execution (undetermined, draft evidence); RCL-011 defines credential-free offline Docker battles and bot-free online submission (undetermined, draft evidence).
• What becomes binding on merge: ADR-0043 binds Docker as the recommended contributor-side distribution, native execution as supported with weaker isolation, and phase separation as the credential boundary. The optional engine.json.clientImage reference is installation guidance, not compatibility state.

Summary

• support both native and Docker execution while recommending Docker for reproducibility and isolation
• separate synchronization, battle, and submission so bot execution has neither external networking nor submission credentials
• require an official Tank Royale release carrying M-005 before publishing and pinning the Rumble Client image
• replace automatic native runtime installation with prerequisite validation

Implementation status

• Add native and Docker runtime distributions rumble-client#6 implements native archives, prerequisite checks, the non-published Docker image, constrained launchers, and cross-platform/Docker CI.
• Validate optional Rumble client image pin rumble-data#6 implements additive validation for the optional immutable client-image pin.
• Battle Runner execution, journal/submission phases, the eligible Tank Royale release, image publication, and final E2E evidence remain open CH-012 tasks.

Verification

• clue validate — OK, 131 artifacts
• git diff --check — OK
• agentic review — clean in-context fallback on commit 364629c54
• hosted check-links — passed
• hosted validate --forbid-changes — expected failure while the active CH-012 workspace remains; this PR is not merge-ready until CH-012 is implemented and digested

Cliewen proposal

• Change ID: CH-012
• Change tier: full continuation
• Plan item served: P-003/M-008
• Proposal location: /changes/CH-012-create-rumble-client/proposal.md
• Agentic review mode and reviewed commit: in-context fallback; 364629c54
• Hosted head reviewed before this update: 364629c545c40ba2e3f14184b7f487fb44f61f42
• Outstanding actionable findings: CH-012 implementation and digest are incomplete; no merge is requested yet

Traceability and Decisions

• Acceptance criteria or capability meaning changed: RCL-008, RCL-010, RCL-011 in CAP-016
• Decision records changed: ADR-0043
• Constraints assessed: C-001 remains satisfied; C-002 is enforced by this branch and human-merge boundary; no behavior evidence is claimed while the new criteria remain draft.

Review boundary

• The branch starts at current main, the intended edits are committed, and the worktree is clean.
• Keep this PR open while the remaining CH-012 tasks are implemented. Update, reverify, and digest it before requesting human merge; no agent will merge it or push to main.