fix(plugins): rename per-turn hook from on_session_end to on_turn_end

[beardthelion]

What does this PR do?

Renames the per-turn plugin hook from on_session_end to on_turn_end in run_agent.py. The hook fired at the end of every run_conversation() call (once per user message), not at actual session boundaries — the name was misleading.

Note: This conflicts with PR #22095 which adds on_turn_start/on_turn_end as NEW hooks while keeping on_session_end firing per-turn. This PR takes the cleaner approach: rename the existing per-turn fire instead of adding redundant hooks. PR #22095 should adapt to use the on_turn_end hook added here.

Related Issue

Discovered during full repo audit (2026-05-14). No pre-existing issue.

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• hermes_cli/plugins.py: Added on_turn_end to VALID_HOOKS
• hermes_cli/hooks.py: Added on_turn_end test fixture
• run_agent.py: Changed per-turn hook fire from on_session_end to on_turn_end
• plugins/disk-cleanup/__init__.py: Migrated registration from on_session_end to on_turn_end
• tests/plugins/test_disk_cleanup_plugin.py: Updated assertion to check on_turn_end

Not changed: google_meet plugin stays on on_session_end (fires at real session boundaries from CLI/gateway).

How to Test

1. scripts/run_tests.sh tests/plugins/ tests/hermes_cli/test_hooks_cli.py -q — all pass
2. Verify disk-cleanup plugin registers on_turn_end hook
3. Verify google_meet plugin still registers on_session_end hook

[teknium1]

Thanks for identifying the naming mismatch. Current main still reproduces it: agent/turn_finalizer.py:489-505 emits on_session_end after every run_conversation() call.

Problems

• This is a public-contract rename, not only a disk-cleanup migration. The documented contract at website/docs/user-guide/features/hooks.md:762-783 and existing registrations in plugins/observability/nemo_relay/__init__.py:406 and plugins/platforms/raft/adapter.py:849 still depend on on_session_end being per-turn.
• Keeping Google Meet on on_session_end does not give it normal session-boundary cleanup: CLI cleanup emits on_session_finalize at cli.py:1166-1171, while Google Meet registers only on_session_end at plugins/google_meet/__init__.py:103.

Suggested changes

• Define a compatibility/migration path for existing on_session_end consumers and update the hook documentation.
• Port the per-turn call to agent/turn_finalizer.py and add tests for per-turn and real-boundary semantics.

Automated hermes-sweeper review.

[beardthelion]

Closing. Main still uses on_session_end as the session-end extraction hook, so renaming it to on_turn_end no longer lines up with current behavior.