The TUI banner reported fewer tools than the classic CLI for the same
config (e.g. 32 vs 38) when an MCP server connected slowly. Root cause:
the agent snapshots `agent.tools` once at build time and never re-reads
the registry. `_make_agent` briefly joins the background MCP discovery
thread (`wait_for_mcp_discovery`, ~0.75s) so fast servers land in that
snapshot, but a server slower than the bound — common for an HTTP MCP
server on first connect — lands *after* the agent is built. Its tools are
then absent from both the agent (uncallable until `/reload-mcp`) and the
banner for the whole session.
The classic CLI doesn't hit this because it re-derives
`get_tool_definitions()` at banner render time (which re-waits for
discovery), so it picks the late tools up.
Fix: after a fresh agent is built and its first `session.info` emitted,
if discovery is still in flight, schedule an off-critical-path daemon that
waits for it to finish, then rebuilds the tool snapshot and re-emits
`session.info` — the same rebuild `/reload-mcp` performs, but automatic.
Both the agent's callable tools and the banner count catch up.
Cache safety: the rebuild runs only while the session is still
pre-first-turn (`_user_turn_count`/`_api_call_count` both 0 → nothing
cached to invalidate). Once the user has sent a message we leave the
snapshot frozen rather than break the cached prompt prefix mid-conversation;
late tools then require an explicit `/reload-mcp` (user-consented), exactly
as today. No-op when discovery finished before the agent build, when the
join times out, when the registry was unchanged, or when the session was
swapped/closed while waiting.
Adds entry.mcp_discovery_in_flight() / join_mcp_discovery() accessors and
covers the matrix (added/none/post-turn/timeout/unchanged/replaced) with
unit tests.
