refactor: name capability runners and evidence by what they prove

[levifig]

Summary

Artifact names describe what they prove, never the work unit that commissioned them. The enclosing Change directory already supplies that provenance, so the prefix was redundant and pointed the wrong way.

• Capability smoke runners renamed by target and context mode. The Cursor runner becomes preflight-cursor-agent-context.mjs, because it is a preflight that refuses rather than a smoke.
• Retained evidence renamed to <target>-<version>-<mode> form. Version stays in the filename: it is the identity of what was proven, not a work reference.
• Runners take an explicit --client, --expected-version and --receipt, validate each input, and publish a receipt atomically only after both the proof and cleanup succeed.
• Marker prefixes become target-scoped: LOAF_CLAUDE_STARTUP_SMOKE_, LOAF_CODEX_STARTUP_SMOKE_, LOAF_OPENCODE_REQUEST_SMOKE_.
• The capability runner unit suite runs in build CI via npm run test:capability-runners.

Rebase note

Reduced from five commits to one, and the base is retargeted from feat/target-adapter-doctor to main.

The four lower commits belonged to #109's stack. The manifest and content-addressed install portions of that stack have since landed in main by another route, so only the unique capability-runner commit is carried here. #109 stays open: its target-adapter ownership doctor check has not landed — main's doctor registers six checks and none of them is checkTargetAdapterOwnership — so it needs its own reconciliation pass.

Evidence

Renaming the marker prefixes invalidated all three retained receipts. The strict validators failed closed on them before re-recording, with installed-smoke evidence does not prove a successful model-visible marker result. Receipts were re-recorded by genuinely re-running each runner against the current native binary, never by editing a marker into a file.

Receipt	Version	Observed marker
claude-code-2.1.218-plugin-startup-smoke.json	2.1.218, pinned in a disposable prefix because global is 2.1.219	LOAF_CLAUDE_STARTUP_SMOKE_82C9A319C829
codex-0.145.0-isolated-startup-smoke.json	0.145.0	LOAF_CODEX_STARTUP_SMOKE_A5533AEA314C
opencode-1.18.4-isolated-request-smoke.json	1.18.4	LOAF_OPENCODE_REQUEST_SMOKE_BB01462EC885

The OpenCode receipt additionally proves plugin_loaded, root_session_lookup_proven, no_auth_supplied and cleanup_succeeded.

Verification

• LOAF_VALIDATE_TYPESCRIPT=1 npm run build
• npm run typecheck
• npm run test — all four packages pass
• npm run test:capability-runners — 21 passed
• Strict capability suite
• loaf check --hook for check-secrets, security-audit, render-drift, ephemeral-provenance
• git diff --check

Out of scope

Two historical records still name the superseded runner and receipt filenames: docs/changes/20260718-installed-distribution-authority/plan.md and docs/changes/20260724-version-agnostic-managed-block/evidence.md. Both are factual accounts of commands that ran under those names, so they are left intact rather than rewritten.