Devaipod hosts the OpenCode web UI in an iframe that is destroyed when
the user switches to a different pod.  If the switch happens while the
agent is still processing, the per-session prompt state persisted in
localStorage may retain the already-submitted text.  When the user
returns and the iframe is recreated, the stale prompt reappears in the
input box.

This is specific to devaipod's iframe-based pod switching -- upstream
OpenCode does not encounter this because the page is not torn down
mid-processing.  The workaround lives in the vendored UI code for now
because that is where the per-session prompt persistence lives.

Extract isStaleSubmittedPrompt() into helpers.ts as a pure function:
on session mount, if the session is idle, the prompt has content, and
that content matches the last user message text, treat it as leftover
from a prior submission and clear it.  Legitimate unsent drafts are
preserved because they won't match any sent message.

Assisted-by: OpenCode (claude-opus-4-6)
Signed-off-by: arewm <arewm@users.noreply.github.com>

The agent health check uses `nc -z` in the workspace container to
detect whether the opencode server is listening. When a custom image
is used that lacks netcat (e.g. the devaipod image itself), every
poll silently fails, the 60-second timeout fires, and the initial
task message is never sent — leaving the agent idle with zero
sessions despite being healthy.

Fall back to `curl` when `nc` is unavailable, since curl is present
in a wider range of images.

Assisted-by: Claude Code (Opus 4.6)
Signed-off-by: arewm <arewm@users.noreply.github.com>