fabro/plan.md

Plan: Use short hex IDs for subagents instead of UUIDs

Summary

GitHub issue #126: Subagent IDs are currently full UUID v4 strings (36 chars, e.g. 550e8400-e29b-41d4-a716-446655440000). These are verbose in CLI output and error-prone when referenced by the LLM in tools like send_input, wait, and close_agent. The codebase already truncates agent IDs to 8 chars for display in multiple places. This change replaces UUID generation with a random 8-char hex string (e.g. a3f1b20c) so the full ID matches what's already displayed.

Files to modify

1. lib/crates/fabro-agent/Cargo.toml

• Add rand.workspace = true to [dependencies]. (rand = "0.8" is already defined in workspace root Cargo.toml; other crates like fabro-cli, fabro-llm, fabro-workflow already use it.)
• Do not remove uuid.workspace = true — it's still used in session.rs:58 for session IDs.

2. lib/crates/fabro-agent/src/subagent.rs

• Line 67: Replace uuid::Uuid::new_v4().to_string() with format!("{:08x}", rand::random::<u32>()).
• This generates 8-char lowercase hex strings with ~4 billion possible values — collision-free within a session.

3. lib/crates/fabro-agent/src/cli.rs

Remove the short_id truncation pattern in 5 places. Since IDs are now 8 chars, short_id == agent_id, so use agent_id directly:

• Line 542 (SubAgentSpawned handler): Remove let short_id = &agent_id[..8.min(agent_id.len())]; and replace {short_id} with {agent_id} in the format string.
• Line 561 (SubAgentCompleted handler): Same removal and replacement.
• Line 574 (SubAgentFailed handler): Same removal and replacement.
• Line 583 (SubAgentClosed handler): Same removal and replacement.
• Line 596 (SubAgentEvent handler, verbose mode): Same removal and replacement.

4. lib/crates/fabro-cli/src/commands/run_progress.rs

Remove the short_id truncation pattern in 2 places:

• Line 1416 (SubAgentSpawned handler): Remove let short_id = &agent_id[..agent_id.len().min(8)]; and replace {short_id} with {agent_id} in the format string.
• Line 1432 (SubAgentCompleted handler): Same removal and replacement.

Step-by-step implementation

1. Add rand dependency to fabro-agent: In lib/crates/fabro-agent/Cargo.toml, add rand.workspace = true to the [dependencies] section (e.g. after the uuid.workspace = true line).

2. Replace UUID generation in subagent.rs: In lib/crates/fabro-agent/src/subagent.rs line 67, change:

   let agent_id = uuid::Uuid::new_v4().to_string();
   

   to:

   let agent_id = format!("{:08x}", rand::random::<u32>());
   

3. Remove short_id truncation in cli.rs: In lib/crates/fabro-agent/src/cli.rs, for each of the 5 occurrences of let short_id = &agent_id[..8.min(agent_id.len())]; (lines 542, 561, 574, 583, 596):

   • Delete the let short_id = ... line.
   • Replace {short_id} with {agent_id} in the corresponding format string on the same match arm.

4. Remove short_id truncation in run_progress.rs: In lib/crates/fabro-cli/src/commands/run_progress.rs, for each of the 2 occurrences of let short_id = &agent_id[..agent_id.len().min(8)]; (lines 1416, 1432):

   • Delete the let short_id = ... line.
   • Replace {short_id} with {agent_id} in the corresponding format string.

Verification

• cargo build --workspace — clean build with no errors.
• cargo test -p fabro-agent — all existing subagent tests pass. Tests use hardcoded IDs like "sa-1", not UUIDs, so no test changes needed.
• cargo clippy --workspace -- -D warnings — no new warnings.
• cargo fmt --check --all — formatting is clean.

Test cases

No new test cases are needed. The existing tests in subagent.rs (e.g. spawn_creates_agent_and_returns_id) already verify that:

• agent_id is non-empty
• The agent can be looked up by its ID
• Spawn/wait/close/send_input work with the generated IDs

The generated IDs will now be 8 chars instead of 36, but the tests don't assert on length or format, so they pass unchanged.