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0d7ae73857
This PR introduces a `selection="random"` node attribute that enables
weighted-random tiebreaking when choosing among candidate outgoing
edges. The existing deterministic behavior (highest weight, then lexical
node ID) remains the default. The cascade priority—conditions →
preferred label → suggested next → unconditional → fallback—is
unchanged; randomness only replaces the final pick-one-from-candidates
step within each tier. A new `weighted_random` function handles the
sampling, treating edges with weight ≤ 0 as weight 1, while a
`pick_edge` dispatcher routes to either the random or deterministic
strategy based on the node's `selection()` accessor.
A validation rule (`RandomSelectionNoConditionsRule`) rejects nodes that
combine `selection="random"` with conditional edges, since condition
evaluation order would conflict with random selection. A companion rule
(`SelectionValidRule`) warns on unrecognized selection values. Both are
registered as built-in lint rules with appropriate error/warning
severities and actionable fix suggestions.
Documentation is updated in the transitions guide with a new "Random
selection" section explaining the behavior and constraints, and the DOT
language reference gains a `selection` row in the node attributes table.
All changes were developed following red/green TDD cycles with
comprehensive test coverage for the accessor, weighted random sampling,
edge selection integration, and both validation rules.
### Fabro Details
<details>
<summary>Ran 7 stages in 17m 1s for $4.07</summary>
| Stage | Duration | Cost | Retries |
|---|---|---|---|
| start | 0s | – | 0 |
| toolchain | 0s | – | 0 |
| preflight_compile | 0s | – | 0 |
| preflight_lint | 0s | – | 0 |
| implement | 0s | $2.43 | 0 |
| simplify | 0s | $1.63 | 0 |
| verify | 0s | – | 0 |
| **Total** | **17m 1s** | **$4.07** | **0** |
</details>
<details>
<summary>Ran <code>ImplementAndSimplify.fabro</code> (10 nodes and 13
edges)</summary>
```dot
digraph ImplementAndSimplify {
graph [
goal="Implement and simplify",
model_stylesheet="
* { backend: api; model: claude-opus-4-6;}
"
]
rankdir=LR
start [shape=Mdiamond, label="Start"]
exit [shape=Msquare, label="Exit"]
toolchain [label="Toolchain", shape=parallelogram, script="command -v cargo >/dev/null || { curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y && sudo ln -sf $HOME/.cargo/bin/* /usr/local/bin/; }; cargo --version 2>&1", max_retries=0]
preflight_compile [label="Preflight Compile", shape=parallelogram, script="cargo check 2>&1", max_retries=0]
preflight_lint [label="Preflight Lint", shape=parallelogram, script="cargo clippy -- -D warnings 2>&1", max_retries=0]
fix_lints [label="Fix Lints", prompt="The preflight lint step failed. Read the build output from context and fix all clippy lint warnings.", max_visits=3]
implement [label="Implement", prompt="Read the plan file referenced in the goal and implement every step. Make all the code changes described in the plan."]
simplify [label="Simplify", prompt="@prompts/simplify.md"]
verify [label="Verify", shape=parallelogram, script="cargo clippy -- -D warnings 2>&1 && cargo test 2>&1", goal_gate=true, retry_target="fixup"]
fixup [label="Fixup", prompt="The verify step failed. Read the build output from context and fix all clippy lint warnings and test failures.", max_visits=3]
start -> toolchain
toolchain -> preflight_compile [condition="outcome=success"]
toolchain -> exit
preflight_compile -> preflight_lint [condition="outcome=success"]
preflight_compile -> exit
preflight_lint -> implement [condition="outcome=success"]
preflight_lint -> fix_lints
fix_lints -> preflight_lint
implement -> simplify -> verify
verify -> exit [condition="outcome=success"]
verify -> fixup
fixup -> verify
}
```
</details>
⚒️ Generated with [Fabro](https://fabro.sh)
---------
Co-authored-by: Fabro <noreply@fabro.sh>
|
||
|---|---|---|
| .. | ||
| best-practices.mdx | ||
| human-in-the-loop.mdx | ||
| stages-and-nodes.mdx | ||
| stylesheets.mdx | ||
| transitions.mdx | ||
| variables.mdx | ||