goal: the initial objective disappears from the timeline after /goal #61332

Description

When /goal <objective> is used in a session, the objective never appears as a user message. The first timeline row is a synthetic kickoff notice rendered as one truncated line:

Goal: 参见计划：...

The rest of the objective cannot be read or expanded from the transcript. This makes the user's initial request look like it disappeared, especially in long sessions.

Steps to reproduce

1. Start a new session.
2. Run /goal <objective> with an objective longer than one line.
3. Look at the top of the timeline.
4. Try to expand the Goal: ... row or find the rest of the text.

Expected

The objective should remain readable in the session, for example as a collapsible goal card or an expandable notice with the full text. Copying it should also be possible.

Actual

Only Goal: <first 120 characters> is shown, then the row is clipped by truncate. The full text exists in the synthetic message's text field, but there is no UI path to it. The session title is also replaced with the first 60 characters of the objective, so the tab and header show the same fragment.

Root cause

• packages/core/src/plugin/goal.ts:411-431 stores the objective in goal storage and creates a synthetic kickoff with description: Goal: ${truncate(text, 120)} instead of a user message.
• packages/session-ui/src/timeline/projection.ts:1179-1186 projects synthetic messages with a description as Notice rows.
• packages/session-ui/src/timeline/session-timeline-row.tsx:574,727-729 renders the notice as a single-line truncate with no expand or copy.
• packages/core/src/plugin/goal.ts:404-409 overwrites the session title with truncate(text, 60).

Additional context

• A real 356-message session export has messages[0].type === "synthetic", metadata.source === "goal", and only one later user message. The initial objective is not present as a user message.
• This is the built-in goal plugin added in feat(core): add /goal with a client-side done check #59437 (v2.2.1+), not a third-party plugin.
• The goal pill also lacks a full-text or copy view; this is tracked separately.

Environment

• OpenCode Desktop v2.2.5 (source checkout 1bf08ae; Desktop and web share the same packages/app renderer).
• Windows desktop app.
• No third-party plugins; this is the built-in goal plugin.