feat(cli): agent-native provisioning with init --agent and agents claim

[wondercreatemaster]

Summary

• closes feat(cli): agent-native provisioning — vouch init --agent plus a claim handshake #606: vouch init --agent --agent-caller <name> provisions an agent-scoped KB, stamps agent.caller as the persistent proposer identity, and writes a local credential (chmod 0600) that is never echoed to stdout
• emits a claim token / vouch agents claim <token> command (plus --json for skills); claiming from a project KB transfers ownership and adopts knowledge through the same review gate as vouch adopt, leaving the agent credential and agent-KB artifacts untouched
• mcp/jsonl/cli fall back to the stamped agent.caller when VOUCH_AGENT is unset

Test plan

• python -m pytest tests/test_agent_provision.py tests/test_adopt.py -q
• python -m ruff check src tests
• python -m mypy src
• full pytest tests/ -q --ignore=tests/embeddings green locally
• CI green on this PR
• manual: vouch init --agent --agent-caller demo --json → credential path exists, stdout has no credential value → cd project && vouch init && vouch agents claim <token> binds and adopts

[plind-junior]

flagging three things before a maintainer spends time on the +987 diff, because two of them are mechanical and one is scope.

CI is red — diff coverage (100% of changed python) is failing, and it is the gate this repo does not waive. worth getting green before review rather than after, since the fix usually moves lines around.

the file list has a gap that matters more than the coverage number: src/vouch/adopt.py is +83/-34 — a substantial rewrite of an existing, load-bearing module — and tests/test_adopt.py is not in the changed-files list at all. the test plan mentions running it, which is good, but running an unchanged test file against rewritten behaviour tells you the old paths still work, not that the new ownership-transfer path does. agents claim transferring ownership and adopting knowledge is the highest-risk thing in this PR and it currently rides on test_agent_provision.py only.

on scope: this introduces a credential file, a claim-token flow, an ownership-transfer path and a new persistent proposer identity, in one PR, alongside a rewrite of adopt. each of those is individually reviewable; together they are not, and the parts have different risk profiles — --agent-caller stamping a persistent proposer identity is a small change to how attribution works, while writing a chmod-0600 credential and transferring KB ownership is a security surface. splitting the credential/claim half from the provisioning half would let the cheap half land now.

last, minor but it is a house convention: the description carries a "Made with Cursor" trailer. this repo is explicit about not attaching AI-tool attribution to contributions — worth dropping it.

happy to review the substance properly once CI is green and the adopt changes have tests; nothing above is a judgement on the approach.

[wondercreatemaster]

Superseded by a replacement PR that addresses the review notes on this one:

• 100% diff coverage (the gate that was red here)
• adopt_kb is additive — personal-fallback adopt is untouched
• ownership-transfer coverage lives in tests/test_adopt.py
• no AI-tool attribution trailer
• rebased onto current test (includes the feat(cli): agent registry — list, pause, resume, revoke, and per-agent audit replay #607 agents group; claim is added there)