test: follow delegated Claude profile resolver path

[Florious95]

Owns the Claude profile-resolver contract red.

• verifies start_agent_at_paths delegates to spawn_agent_window
• verifies the shared spawn path invokes prepare_provider_profile_launch_from_json
• test-only; no product behavior change

Base: five-provider-PR stack head 7e2c65d.

[Florious95]

Absorption audit: this PR is fully present in the composed release v0.5.69 (peeled SHA 6e9391d5374bc669ec48bfce11d785c0db97fea0) and carried by v0.5.71 (ad1f1874144066c4bf48e0c2e88801c1c7edaf4b). Composition receipt patch-id matches: 2fbb497b→7eb18f28c9d426167b255d56411382273771fe38; the composed release receipt/history records the same exact Claude resolver guard bytes. Closing without merge; the stale stacked-base nonzero diff is not evidence against absorption. The frozen head before closure is 2fbb497b2001bbac120c2364c2f9207e32a8b0b7.