The crew starts every run through one agent-runner seam, with today's CLI as its first runner #12122

Done looks like:

• src/crew/agent_runner.ts defines the runner: start a run in a sandbox with a brief, stream its steps, report spend, pauses and end, as plain data in and out
• src/crew/claude.ts implements it with no change in behaviour: same argv, same env, same outcomes
• runner.ts, dispatch.ts, one_shot.ts and conversation.ts call the seam, and none of them imports claude.ts directly
• A test fails if a module outside the runner implementations imports claude.ts
• bun test is green with no existing test changed except imports

Files: src/crew/agent_runner.ts, src/crew/claude.ts, src/crew/runner.ts, src/crew/dispatch.ts, src/crew/one_shot.ts, src/crew/conversation.ts, test/agent-runner-seam.test.ts

Part of the owner's ask #12068 (AI agnostic). Keep this pull to the files named; earlier tries went red by spreading into src/flow, src/core/events and src/boards. A new process start must be listed in test/spawn-sites.test.ts (and test/spawn-pipes.test.ts) with its reason. The branch mason/12068-the-forge-is-ai-agnostic-you-connect-you (f580581a93e3) holds earlier work to borrow from, not to merge whole.