Fix Vanishing Chats and Messages from Remote

[MrnoRac]

In the remote web UI two bugs appear for chats whose stored :id field has drifted from their :chats map key:

1. Chat vanishes from the list — it's missing from the sidebar and disappears again on reload, even though it's fully loaded with messages and reachable via GET /api/v1/chats/<id>.
2. Chat loses all messages when switching tabs — first open shows everything, but switching away and back renders it empty

Reproducible on versions:

• eca (server): master @ efd534ea6 (ECA_VERSION 0.142.2)
• eca-web: 543b428 (eca-webview submodule 1790003)
• eca-emacs: 20260622.1430 (also reproduced on 20260608.2031)

Setup:** an ECA server with remote.enabled: true, an editor session (e.g. eca-emacs) with at least two pre-existing chats that have message history, and the web UI (web.eca.dev or a local eca-web) connected to it.

Bug 1 — chat vanishes from the list / on reload:

1. In the editor, /resume (or /sessions) an existing chat with history.
2. In the web UI it appears live in the sidebar.
3. Reload the web page → the resumed chat is gone from the sidebar, even though GET /api/v1/chats/<id> still returns it with all its messages.

Bug 2 — chat loses messages on tab switch:

1. In the web UI, open chat 1 → its messages render.
2. Open chat 2 → its messages render.
3. Switch back to chat 1 → empty (no messages). Switch back to chat 2 → also empty.
4. Switching to a different connection/session and back makes the first open of each chat show its messages again — then it breaks the same way on the next switch.

Proposed Fix

Treat the map key as the authoritative id everywhere in the remote handlers as is specified here:
src/eca/features/chat.clj:1967:

"The map key is used as the authoritative :id because legacy DB rows may have been persisted without an :id inside the value, and clients need a non-nil id to call chat/open."

src/eca/db.clj:326:

"Ensures every chat value carries its map key as :id, so readers can rely on it. Heals legacy rows persisted before chats were seeded with an :id."

So...

• handle-list-chats / session-state: iterate :chats pairs, filter editor-open by key, report the key as :id
• handle-get-chat: return the requested path-param key as :id

Cannot affect forks (they already have :id == key).

Tests

Added regression tests in handlers_test.clj: a chat whose :id field ≠ its key, marked editor-open, must appear in handle-list-chats (reported by key) and round-trip through handle-get-chat with the key. bb test green.

Note / follow-up

This is just in case drift happens somewhere else, but it's probably a good idea to fix that drift there too.. it seems to happen in eca-emacs on /resume for example.

• I added a entry in changelog under unreleased section.
• This is not an AI slop.
• Messed around with the checklist :)

[MrnoRac]

I tried to follow the patterns I saw around the repo, but let me know if anything needs changing.