feat: distinguish between a session name and its first prompt

[akolotov]

Summary

This PR distinguishes between a session's metadata-derived name and its first prompt by introducing a separate session_name field in session data.

Before this change, first_message was overloaded:

• sometimes it held a true session title from agent metadata
• sometimes it held the first user prompt

That made the model ambiguous and forced the UI to guess whether it was rendering a real session name or just fallback prompt text.

This PR separates those concerns:

• session_name now stores a trusted metadata-derived session name
• first_message remains the fallback prompt/display text

Trusted session_name sources in this PR:

• Claude Code: custom-title
• Codex: thread_name
• OpenCode: SQLite session title

Why This Functionality Is Added

The detail view and session lists need to represent two different concepts cleanly:

• the actual session name when the underlying tool provides one
• the first prompt when no true name exists

Without a separate field, the UI cannot tell these apart. That causes several problems:

• session details may show the first prompt as if it were the session name
• future naming logic becomes harder to reason about
• search and display logic are forced to treat one field as two different kinds of data

By introducing session_name, the app can now:

• prefer real session names where they exist
• keep using the first prompt as a fallback summary where needed
• support the detail panel rule of AI title -> session_name -> empty

User-Facing Behavior

Session Details

The detail panel now follows this logic for the Name row:

• if an AI-generated name exists in local storage, use it
• otherwise, use session_name
• otherwise, show no name value and keep the Generate AI Name action available

This is intentional: the detail panel is now strict about showing a real name, not the first prompt.

Projects / All Sessions / Related Views

List-style display surfaces continue to show the best available session label, now with explicit fallback:

• session_name || first_message

This preserves the existing UX expectation that every session row should still show something meaningful about what the session is about.

Search

Search now considers both:

• session_name
• first_message

This preserves discoverability whether the user remembers the formal session title or the original first prompt.

Why This Does Not Break Anything

This change is intentionally backward-compatible in behavior.

1. Existing sessions without session_name still work

Most tools do not provide a reliable metadata title. For those sessions:

• session_name is simply empty
• the UI falls back to first_message in list/card/search surfaces

So sessions that previously displayed correctly continue to display correctly.

2. No removal of first_message

first_message is not removed or repurposed into something incompatible. It remains available everywhere it was before, and continues to power fallback labeling and prompt-based discovery.

The change is additive in the data model:

• new field: session_name
• existing field preserved: first_message

3. Detail panel behavior becomes stricter by design, not broken

The detail panel now prefers:

• AI-generated title
• metadata session name
• empty

This is a deliberate semantic improvement. It avoids showing the first prompt as if it were a true session name. The action to generate an AI name remains available, so no capability is lost.

4. Search remains compatible

If title text moved entirely out of first_message without updating search, users could lose the ability to find sessions by title. This PR avoids that by explicitly searching both session_name and first_message.

So search behavior is preserved and improved.

5. Cloud and related displays stay consistent

Cloud-facing display and serialization now also prefer the best available label. That avoids local/cloud divergence for agents that provide a trusted session name.

Implementation Notes

• Added session_name population in session loaders for Claude Code, Codex, and OpenCode
• Preserved first_message as prompt/display fallback text
• Updated main UI display surfaces to use session_name || first_message
• Updated detail panel to use AI title -> session_name -> empty
• Updated search/filter scoring to include both name and first prompt

Risk Assessment

Risk is low because:

• the change is mostly a data-model clarification
• fallback behavior is preserved in the main UI surfaces
• no destructive migration is required
• untrusted tools are not forced into a fake session_name

The main semantic change is limited to the detail panel, where showing only a real name is the intended new behavior.