herd spawn / agent start: default --account to the caller's cswap account (RT-237)

[m4ttheweric]

Problem

A shepherd running under cswap run N has CLAUDE_CONFIG_DIR pointing at that account's session profile. rt herd spawn (and rt agent start) with no --account sent nothing to the daemon, which launched a bare claude on the global default profile. When the default profile is a different account, every worker silently ran as that account.

Fix

• callerCswapAccount (lib/cswap.ts): when CLAUDE_CONFIG_DIR is set, runs cswap list --json in the caller's env and returns the active account's email.
• rt herd spawn fills a missing --account from it.
• rt agent start does the same for claude launches only; codex (by flag or agent.provider) is untouched since it rejects --account.
• Default-profile callers are unchanged (no cswap call, no account passed), so agent.claude.account still applies there.
• Explicit --account always wins.

Verification

• New unit tests in lib/__tests__/cswap.test.ts, lib/__tests__/herd-cli.test.ts, commands/__tests__/agent.test.ts.
• e2e/tests/herd.test.ts and e2e/tests/agent.test.ts green.
• Against real cswap with account 1's session dir set, resolves to account 1 while the global default is account 4.

🤖 Generated with Claude Code

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 8577a1c and 6a7acea.

📒 Files selected for processing (9)

• commands/__tests__/agent.test.ts
• commands/agent.ts
• commands/herd.ts
• lib/__tests__/cswap.test.ts
• lib/__tests__/herd-cli.test.ts
• lib/command-tree-def.ts
• lib/cswap.ts
• website/docs/reference/agent.mdx
• website/docs/reference/herd/spawn.mdx

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