T10 — migration and compatibility

Captured 2026-10-19 on feat/issue-496-gateway, from cli/ with THE_LOOP_CLI_CONFIG unset (this machine's own instance sets it; one unrelated lifecycle test reads it).

cd cli && uv run python -m pytest -q tests/test_hosted_reconcile.py tests/test_core_lifecycle.py tests/test_gateway_client_integration.py
32 passed in 2.06s
make validate
VALID   skills/the-loop/templates/collaborators.yaml
VALID   .the-loop/cli-config.yaml
VALID   skills/the-loop/templates/cli-config.yaml
VALID   skills/the-loop/templates/gateway-config.yaml

• An instance config without a gateway block hosts the receiver, the poller and the listener exactly as before (test_gateway_hosted_integration.py::test_an_instance_without_a_gateway_block_hosts_the_receiver_poller_and_listener_as_before, and the hosted-reconcile and lifecycle suites unchanged in behaviour; enabled_services gains the additive gateway-client key).
• Adding the block adds gateway-client and drops only the Slack listener; the receiver and the poller follow their own blocks (…::test_an_instance_with_a_gateway_block_keeps_its_receiver_and_poller_and_loses_only_the_listener; amended on the PR 2026-10-19 — the first landing hosted the client alone). The Slack poll reader is off behind a gateway (test_channels_integration.py, the watcher scenario). The gateway's own GitHub/Jira polling is opt-in, off in the template.
• The cli-config.schema.json change is additive: the repository's dogfood config and the templates validate (make validate).
• The store carries a schema_version row (SqliteStore.schema_version()), asserted in test_gateway_store.py::test_offsets_survive_a_reopen.
• A behaviour change for Slack readers in poll mode (found in T4, 2026-10-19): an instance that read its threads with read.mode: poll took every reply in a bound thread as input. Under a gateway Slack arrives over Socket Mode only, where the issue-389 rule holds — a plain reply is not-addressed and the mention arrives as app_mention — so an app installed before issue-389 (no app_mentions:read) hears no reply until the manifest is re-applied and the app reinstalled. Documented in the capability and raised with the author on the ticket.
• A fresh gateway replayed an item's history (found 2026-10-19 answering the author's migration question on the PR): the instance poller baselines an armed item's existing thread at first sight; the gateway's poller stored every unseen comment, so its first cycle would have turned the whole history of every armed item into deliveries. Fixed: poll_known on the ledger, the thread marked seen at first sight, the presence alone stored (test_gateway_poll_integration.py::test_a_new_gateway_baselines_an_items_existing_thread_at_first_sight). The move itself is written up in docs/guide/gateway.md.