Make the project-memory runtime fixture test skill behavior #305

Purpose

Make the paired runtime fixture discriminate the installed project-memory skill behavior from instructions supplied by the fixture prompt.

A live run at repository source dddeb94 showed that Claude Code 2.1.273 and Codex CLI 0.154.0 both pass the exact activation, non-trigger, output, and cleanup contracts. However, the activation prompts already name the client-specific file, exact headings, exact lines, merge rule, nested scope, and forbidden cross-client output. The run proves that each client can follow that prompt. It does not prove that the shared skill supplies the missing Codex contract. The committed audit still reports adapter-required because the skill names only CLAUDE.md and has no merge-existing or nested AGENTS.md contract.

Acceptance criteria

• Replace or add an activation prompt that supplies the project facts but does not restate the client-specific output and merge contract.
• Keep the existing verifiers for preserved guidance, root and nested scope, cross-client output rejection, unrelated-file immutability, non-trigger behavior, and cleanup.
• Run the revised fixture through isolated current Claude and Codex clients and record the source revision and client versions.
• Treat the first sandbox namespace failure separately from skill behavior; use the documented nested-runtime fallback when required.
• Add an adapter only if the discriminating run proves that the shared skill cannot meet the Codex contract.

Parent: #236

Receipt: wake-20260916T1505-6e72ca