External workspaces (runtime=external) lose their workspace_auth_token
the moment the create modal closes — the token is unrecoverable from
any later DB read. Operators who lost their copy or want to respond to
a suspected leak had no recovery path short of recreating the workspace
(which also breaks cross-workspace delegation links + memory namespace).
This PR adds two endpoints + a Config-tab section that surfaces them:
POST /workspaces/:id/external/rotate
Revokes any prior live tokens, mints a fresh one, returns the same
ExternalConnectionInfo payload Create returns. Old credentials stop
working immediately — the previously-paired agent will fail auth on
its next heartbeat (~20s).
GET /workspaces/:id/external/connection
Returns the connect block with auth_token="". For the operator who
just needs to re-find PLATFORM_URL / WORKSPACE_ID / one of the
snippets without invalidating the live agent.
Both reject runtime ≠ external with 400 + a hint pointing at /restart
for non-external runtimes (which mints AND injects into the container).
## Why a flag isn't needed
The endpoints are purely additive — Create's behavior is unchanged.
Existing external workspaces don't see anything different until an
operator clicks the new buttons.
## DRY refactor
Extracted BuildExternalConnectionPayload() in external_connection.go
as the single source of truth for the connect payload shape. Create,
Rotate, and GetExternalConnection all call it. Adds a snippet once →
all three endpoints emit it. Trims trailing slash on platform_url so
no double-slash sneaks into registry_endpoint.
## Canvas
ExternalConnectionSection mounts in ConfigTab when runtime=external.
Two buttons:
- "Show connection info" (cosmetic) — fetches GET /external/connection
- "Rotate credentials" (destructive) — confirm dialog explains the
impact, then POST /external/rotate
Both reuse the existing ExternalConnectModal so operators don't learn
a second snippet UX.
## Coverage
10 Go tests:
- Rotate happy path (revoke + mint order, payload shape, broadcast event)
- Rotate refuses non-external runtimes (400 with restart hint)
- Rotate 404 on unknown workspace + 400 on empty id
- GetExternalConnection happy path (auth_token="", same payload shape)
- GetExternalConnection refuses non-external + 404 on unknown
- BuildExternalConnectionPayload — placeholder substitution + trailing
slash trimming + blank-token contract
6 canvas tests:
- both action buttons render
- "Show" calls GET /external/connection and opens modal
- "Rotate" opens confirm dialog before firing POST
- Cancel dismisses without rotating
- Confirm POSTs and opens modal with returned token
- API failures surface as visible error chips
Migration: existing external workspaces gain new abilities; no data
migration. The DRY refactor preserves byte-identical Create response
shape (8 ConfigTab tests + all existing handler tests still pass).
Closes#319.
b375252dc8