@W-22203675 fix: generate session-meta.json when starting agent preview session

[sreckomileta]

@W-22203675@

What does this PR do?

What issues does this PR fix or reference?

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Functionality Before

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Functionality After

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Testing Setup Notes

[franciscoperezsammartino]

Got this from claude:

Code Quality

sessionManager.ts

• Duplication: The exact same 7-line block is copy-pasted in two places — startSession and what appears to be a
  restart path (~line 252). This is a clear candidate for extraction into a private helper like
  writeSessionCache(agentSource, isLiveMode).
• Type cast smell: sessionType as 'live' | 'simulated' | 'published' — the cast exists because the ternary produces
  a string. You can get rid of it by typing the variable explicitly:
  const sessionType: 'live' | 'simulated' | 'published' =
  agentSource === AgentSource.SCRIPT ? (isLiveMode ? 'live' : 'simulated') : 'published';
• Comment style: The inline comments (// Write session-meta.json so SF CLI...) are descriptive of what rather than
  why, which goes against the project conventions observed elsewhere. Consider dropping them since the function name
  createPreviewSessionCache is self-documenting.
• No error handling: If createPreviewSessionCache throws (e.g., filesystem error, missing project path), it will
  bubble up and abort the session start. A try/catch with a logged warning may be safer — failing to write the cache
  file is probably not fatal enough to crash the whole session start.

[franciscoperezsammartino]

in endSession, should we delete this session-meta.json as well?

[sreckomileta]

When you end a session using the "sf agent preview end" command, it is no longer listed when running "sf agent preview sessions"; however, all the files are retained. I believe that if the command deletes the other files, it should also delete this one.

[franciscoperezsammartino]

right, the CLI command does delete this. But if you stop the session from VS code, should that delete the session as well?