feat(cli): support session forking and history loading in CLI

[srimon12]

Adds a --fork <session_id> CLI flag to allow initializing a new session from an existing parent session's history.

This copies events from the specified parent session to the new child session on startup and records a SessionFork event.

Key Changes:

• Added a --fork option to CLI arguments.
• Pre-populates the new session's event history with the parent session's events from the backend store on initialization.

Summary by CodeRabbit

• New Features

  • Added a new --fork option to clone an existing session into a fresh session ID.
  • When used without other input, the app now confirms the cloned session ID and exits cleanly.
  • The TUI now starts from the cloned session when forking is used.

• Bug Fixes

  • Prevents creating a fork from an empty session.
  • Ensures the copied session history is preserved under the new session ID before continuing.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: afdd7d32-1a70-44e0-9086-0174551723a3

📥 Commits

Reviewing files that changed from the base of the PR and between 34c9ab8 and 09bd1ef.

📒 Files selected for processing (2)

• microagents-cli/src/main.rs
• microagents-events/src/lib.rs

📝 Walkthrough

Walkthrough

Adds a --fork <ID> CLI flag to microagents-cli. A new fork_session async function clones a parent session's events into a new UUID-backed session. main computes a resolved_session_id from either the fork result or --session-id, and both the headless and TUI paths use this resolved ID.

Fork Session Feature

Layer / File(s)	Summary
--fork arg, fork_session helper, and resolved_session_id wiring microagents-cli/src/main.rs	Args gains fork: Option<String> for --fork <ID>; fork_session loads parent session events, rejects empty sessions, generates a new UUID, and writes cloned events; main derives resolved_session_id from the fork or --session-id, prints and exits if only forking, and passes the resolved ID to both headless and TUI run paths.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐇 Hop! A session splits in two,
The past is cloned, the future new.
A UUID born from one before,
Fork and run — then run some more.
What once was lost can start again,
Down the rabbit hole... and then! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: adding CLI session forking and loading prior session history.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@microagents-cli/src/main.rs`:
- Around line 140-156: The fork flow in main currently clones parent events and
returns the new session id, but it never persists the SessionFork marker event.
After the child session is created in the event replay loop, add a write for the
SessionFork event through storage so the lineage is recorded distinctly from a
normal resumed session. Use the existing session-writing path in main alongside
the SessionInit and other event handling to place this marker at the right point
in the fork process.
- Around line 163-169: The forked startup logic in main.rs is treating
`--session-id` as the only way to continue into the TUI after `fork_session`,
which makes plain `--fork <parent>` exit early unless an unrelated value is
passed. Update the `resolved_session_id` handling so the forked TUI path uses
`Some(new_sid)` when `args.fork` is present and no prompt is provided, and
reserve the early return only for an explicit clone-only mode if you add one.
Keep the fix centered on `fork_session`, `resolved_session_id`, and the
`args.prompt` / `args.session_id` branch.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 8d1dc15b-0b86-4d31-acde-a6eaaebc6a2f

📥 Commits

Reviewing files that changed from the base of the PR and between a5408c9 and 34c9ab8.

📒 Files selected for processing (1)

• microagents-cli/src/main.rs