Record the loose end the taskNote outage exposed, and the last of its checks

A session whose transcript will not parse is skipped with only a log line, so
from the phone it is indistinguishable from an idle unresponsive one. That is
why the outage needed a report from Bryan rather than showing itself. The
cause is fixed; the class is not, and it is the "design the unknown state
first" rule rather than a bug in one code path.

Also rustfmt on the parse path, which the fix landed unformatted.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

TODO.md

@@ -33,3 +33,21 @@ one in place when it turns out to need a decision.
       that would work today, for Claude sessions, and it is the option that was
       not chosen.
 
+
+## A session the server could not load
+
+- [ ] **A session whose transcript will not parse is skipped with nothing but a
+      log line, and from the phone it looks exactly like an idle unresponsive
+      one.** `SessionManager::new` catches a failing `launch` and logs
+      "couldn't relaunch session <id>", so the session has no pump and no
+      driver: no status, no history, nothing sendable. That is what the
+      `taskNote` incident (fd71d87) looked like from Bryan's phone, and why it
+      needed a report from him rather than being visible in the app.
+      `Event::Unreadable` removes the cause that time, but not the class — an
+      unreadable `process.json`, a provider edited away and an unreachable host
+      all reach the same place.
+      This is the "design the unknown state first" rule: a session the server
+      could not load is not a session with nothing to say, and only the phone
+      can show the difference. It needs a status the wire can carry for it —
+      the failure with its reason, reported on the session itself — rather than
+      the reader having to tell it apart from silence.

server/src/session/transcript.rs

@@ -353,9 +353,8 @@ impl<'a> Indexed<'a> {
                     #[serde(rename = "type")]
                     kind: Option<String>,
                 }
-                let place: JustPlace = serde_json::from_str(line).with_context(|| {
+                let place: JustPlace = serde_json::from_str(line)
-                    format!("bad transcript line in {}", self.path.display())
+                    .with_context(|| format!("bad transcript line in {}", self.path.display()))?;
-                })?;
                 // Debug rather than a warning: a transcript written against a
                 // newer build has one of these per line it wrote, and the row
                 // on the phone is where this is actually reported.