Replaces the source-string-only test from #1898 with @Michaelyklam's functional
regression from #1904. The new test creates two synthetic profile homes with
distinct SOUL.md contents, runs _run_agent_streaming() three times on the same
session (profile A, profile A, profile B), and asserts that the profile switch
rebuilds the agent and uses profile B's cached SOUL prompt — proving the
user-visible failure mode directly rather than relying on cache-signature shape.
Kept source checks that _profile_home is resolved before the signature and
included as `_profile_home or ''` for stable empty-home behavior, since the
functional test alone wouldn't catch ordering regressions.
Co-authored-by: Michael Lam <Michaelyklam1@gmail.com>
Same-session profile switches reused cached AIAgent from previous profile,
silently leaking the old persona's SOUL.md / system prompt into the new
profile's turns. session_id stays stable across profile switches, and the
signature didn't include the active profile home, so every signature input
matched and the stale agent was returned from SESSION_AGENT_CACHE.
Append _profile_home to the signature blob so profile switches force a
cache miss and a fresh agent build under the new HERMES_HOME (which
triggers a fresh load_soul_md() call).
Tests: 3 source-string regressions guarding the signature contract,
ordering, and empty-home fallback.
Closes#1897
Co-authored-by: Hermes Agent <agent@hermes.local>
nesquena-hermes