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fabro/plan.md
brynary-fabro[bot] c119bf3c79 Use short hex IDs for subagents instead of UUIDs (#128) 
This PR updates subagent ID generation to use short 8-character hex
strings instead of full UUID v4 strings. Previously, subagent IDs were
36-character UUIDs (e.g. `550e8400-e29b-41d4-a716-446655440000`), which
were verbose in CLI output and unwieldy when the LLM needed to reference
them in tools like `send_input`, `wait`, and `close_agent`. The new
format generates IDs like `a3f1b20c` — compact, human-readable, and with
~4 billion possible values, effectively collision-free within a session.

The change is made at the source in `subagent.rs`, where UUID generation
is replaced with `format!("{:08x}",
uuid::Uuid::new_v4().as_fields().0)`. Because IDs are now inherently 8
characters, the display-layer truncations in `cli.rs` (5 occurrences)
and `run_progress.rs` (2 occurrences) are redundant and have been
removed — `agent_id` is used directly in format strings instead of a
`short_id` slice.

### Plan Summary

- **Replace UUID generation** in `subagent.rs`: use the first field of a
UUID v4 formatted as 8-char lowercase hex, yielding IDs like `a3f1b20c`
instead of full 36-char UUIDs
- **Remove `short_id` truncation** in `cli.rs` (5 places) and
`run_progress.rs` (2 places): since IDs are now already 8 chars, the
`let short_id = &agent_id[..8.min(agent_id.len())]` pattern is
eliminated and `{agent_id}` is used directly in all format strings
- No test changes required — existing tests use hardcoded IDs like
`"sa-1"` and don't assert on ID length or format

<details>
<summary>Full plan</summary>

````md
The plan has been written to `/home/daytona/workspace/plan.md`.

It covers:
- **4 files to modify**: `fabro-agent/Cargo.toml` (add `rand` dep), `subagent.rs` (replace UUID with 8-char hex), `cli.rs` (remove 5 `short_id` truncations), `run_progress.rs` (remove 2 `short_id` truncations)
- **Step-by-step implementation** with exact line references and before/after code
- **Verification commands** to confirm correctness
- **Test case analysis** explaining why no test changes are needed
````

</details>

### Fabro Details

<details>
<summary>Ran 3 stages in 18m 46s for $0.57</summary>

| Stage | Duration | Cost | Retries |
|---|---|---|---|
| start | 0s | – | 0 |
| plan | 1m 28s | $0.57 | 0 |
| implement | 17m 6s | – | 0 |
| **Total** | **18m 46s** | **$0.57** | **0** |

</details>

<details>
<summary>Ran <code>GhImplement.fabro</code> (4 nodes and 3
edges)</summary>

```dot
digraph GhImplement {
    graph [
        goal="Implement a GitHub issue",
        model_stylesheet="
            * { model: claude-opus-4-6; }
        "
    ]
    rankdir=LR

    start [shape=Mdiamond, label="Start"]
    exit  [shape=Msquare, label="Exit"]

    plan [label="Plan", prompt="Fetch the GitHub issue from the goal using: gh issue view $goal --json title,body,labels,comments\n\nRead the issue title, description, and any comments carefully. Analyze what code changes are needed to resolve the issue.\n\nWrite a detailed implementation plan to plan.md that includes:\n- Summary of the issue\n- Files to create or modify\n- Step-by-step implementation approach\n- Test cases to add or update\n\nThe plan should be specific enough for another agent to implement without seeing the original issue.\n\nRespond with the location of the plan file (plan.md)."]

    implement [label="Implement", shape=house, stack.child_workflow="fabro/workflows/implement/workflow.fabro", manager.max_cycles=100]

    start -> plan
    plan -> implement [fidelity="summary:high"]
    implement -> exit
}

```

</details>

⚒️ Generated with [Fabro](https://fabro.sh)

---------

Co-authored-by: Fabro <noreply@fabro.sh>
2026-03-20 21:38:16 -04:00

4 KiB
Raw Blame History

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-workflows 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.