fix(tui): "extracting graph..." spinner never cleared after spawn_graph_extraction

[bug-ops]

Problem

The TUI status bar shows extracting graph... spinner indefinitely after each turn where graph extraction is triggered.

Root cause

In crates/zeph-core/src/agent/persistence.rs:

// line 473
let _ = self.channel.send_status("extracting graph...").await;  // spinner ON

// line 489
memory.spawn_graph_extraction(...);  // fire-and-forget tokio::spawn — returns immediately
// ← no send_status("") here — spinner is NEVER cleared

spawn_graph_extraction() spawns a background task and returns immediately. The status "" is only reset inside check_summarization() (line 527), which is a separate code path. After graph extraction is spawned, the status bar is never cleared.

Additionally, if the extraction LLM times out (extraction_timeout_secs = 15 default), the timeout is silently swallowed with only a tracing::warn — the spinner still stays visible.

Fix options

Option A (simplest): Clear status immediately after spawn_graph_extraction():

memory.spawn_graph_extraction(...);
let _ = self.channel.send_status("").await;  // clear right away

This is honest — the task is background, the UI shouldn't pretend to be waiting for it.

Option B (accurate): Pass a oneshot::Sender into the background task and clear the status when the task completes or times out:

let (done_tx, done_rx) = tokio::sync::oneshot::channel();
memory.spawn_graph_extraction(..., Some(done_tx));
// inside spawn: done_tx.send(()) on completion/error/timeout
// in agent: await done_rx then send_status("")

This would require making the agent block on extraction, defeating the fire-and-forget design.

Recommended: Option A. Since extraction is intentionally async and non-blocking, the status message should reflect that — e.g. change the label to "saving to graph..." and clear it immediately after spawn, or simply remove the send_status call entirely for this path.

Affected code

• crates/zeph-core/src/agent/persistence.rs lines 473–489

Steps to reproduce

1. Enable graph memory in config ([memory.graph] enabled = true)
2. Start a conversation — after each turn the TUI shows extracting graph...
3. The spinner never goes away until the next status event overwrites it