fabro(01KM6RYWXA9TZ4GFKQT99NF7A7): plan (success)

Fabro-Run: 01KM6RYWXA9TZ4GFKQT99NF7A7
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plan.md

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+# Plan: Use short hex IDs for subagents instead of UUIDs
+
+## Issue Summary
+
+GitHub Issue #126: Subagent IDs are currently full UUID v4 strings (36 chars, e.g. `550e8400-e29b-41d4-a716-446655440000`). These appear in CLI output and must be passed back by the LLM to tools like `send_input`, `wait`, and `close_agent`. A shorter, random 8-character hex string (e.g. `a3f1b20c`) is easier to read and less error-prone. The codebase already truncates agent IDs to 8 chars in multiple display locations — this change makes the canonical ID match what's already shown.
+
+## Files to Modify
+
+1. **`lib/crates/fabro-agent/Cargo.toml`** — Add `rand` dependency (already a workspace dep).
+2. **`lib/crates/fabro-agent/src/subagent.rs`** — Replace UUID generation with 8-char hex.
+3. **`lib/crates/fabro-agent/src/cli.rs`** — Remove 5 instances of `short_id` truncation; use `agent_id` directly.
+4. **`lib/crates/fabro-cli/src/commands/run_progress.rs`** — Remove 2 instances of `short_id` truncation; use `agent_id` directly.
+
+No files need to be created.
+
+## Step-by-step Implementation
+
+### Step 1: Add `rand` to `fabro-agent` dependencies
+
+In `lib/crates/fabro-agent/Cargo.toml`, add `rand.workspace = true` to `[dependencies]`. The `rand = "0.8"` workspace dependency already exists in the root `Cargo.toml`.
+
+Note: Do **not** remove `uuid` — it is still used for session IDs in `session.rs:58`.
+
+### Step 2: Replace UUID with random hex in `subagent.rs`
+
+In `lib/crates/fabro-agent/src/subagent.rs`, line 67, change:
+
+```rust
+let agent_id = uuid::Uuid::new_v4().to_string();
+```
+
+to:
+
+```rust
+let agent_id = format!("{:08x}", rand::random::<u32>());
+```
+
+This generates an 8-character lowercase hex string from a random `u32` (~4 billion possible values, effectively collision-free within a session).
+
+### Step 3: Remove `short_id` truncation in `cli.rs`
+
+In `lib/crates/fabro-agent/src/cli.rs`, there are 5 occurrences of `let short_id = &agent_id[..8.min(agent_id.len())];` (lines 542, 561, 574, 583, 596). Since the agent ID is now exactly 8 chars, these truncation lines are redundant. For each occurrence:
+
+- Remove the `let short_id = ...` line.
+- Replace all uses of `short_id` with `agent_id` in the surrounding format strings.
+
+The 5 locations are inside match arms for:
+1. `AgentEvent::SubAgentSpawned` (line 542)
+2. `AgentEvent::SubAgentCompleted` (line 561)
+3. `AgentEvent::SubAgentFailed` (line 574)
+4. `AgentEvent::SubAgentClosed` (line 583)
+5. `AgentEvent::SubAgentEvent` (line 596, inside `if verbose` guard)
+
+### Step 4: Remove `short_id` truncation in `run_progress.rs`
+
+In `lib/crates/fabro-cli/src/commands/run_progress.rs`, there are 2 occurrences of `let short_id = &agent_id[..agent_id.len().min(8)];` (lines 1416, 1432). For each:
+
+- Remove the `let short_id = ...` line.
+- Replace `short_id` with `agent_id` in the surrounding format strings.
+
+The 2 locations are inside match arms for:
+1. `AgentEvent::SubAgentSpawned` (line 1416)
+2. `AgentEvent::SubAgentCompleted` (line 1432)
+
+## Verification / Test Cases
+
+No new tests are needed. Existing tests use hardcoded IDs (like `"sa-1"`, `"nonexistent-id"`, `"x"`) and don't depend on the UUID format. The spawn test (`spawn_creates_agent_and_returns_id`) asserts the ID is non-empty, which still passes.
+
+Run these commands to verify:
+
+1. `cargo test -p fabro-agent` — all subagent tests pass
+2. `cargo test -p fabro-cli` — run_progress tests pass
+3. `cargo clippy --workspace -- -D warnings` — no warnings
+4. `cargo build --workspace` — clean build