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Update 47 MDX doc pages, OpenAPI spec, SVG diagram, language grammar, frontend demo data, marketing page, skills, and README to use .fabro extension. Add "fabro" to fileTypes in language grammars. Document stack.child_workflow alongside stack.child_dotfile. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
119 lines
4.3 KiB
Text
119 lines
4.3 KiB
Text
---
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title: "Parallel Review"
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description: "Fan-out, fan-in, join policies, and merge nodes"
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---
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This tutorial runs three code review perspectives in parallel — security, architecture, and quality — then merges the results into a single report.
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## The workflow
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<Frame>
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<img src="/images/tutorial-parallel-review.svg" alt="Parallel Review workflow: Start → Fan Out → Security Audit, Architecture Review, Code Quality → Merge → Final Report → Exit" />
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</Frame>
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```dot title="parallel.fabro"
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digraph Parallel {
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graph [goal="Perform a multi-perspective code review"]
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rankdir=LR
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start [shape=Mdiamond, label="Start"]
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exit [shape=Msquare, label="Exit"]
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fork [label="Fork Analysis", shape=component, join_policy="wait_all", error_policy="continue"]
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security [label="Security Audit", prompt="Examine the codebase for security concerns: hardcoded secrets, injection risks, unsafe dependencies. List findings as bullet points.", shape=tab, reasoning_effort="low"]
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architecture [label="Architecture Review", prompt="Assess the codebase architecture: separation of concerns, dependency structure, modularity. List findings as bullet points.", shape=tab, reasoning_effort="low"]
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quality [label="Code Quality", prompt="Check code quality: naming conventions, dead code, test coverage gaps, error handling. List findings as bullet points.", shape=tab, reasoning_effort="low"]
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merge [label="Merge Findings", shape=tripleoctagon]
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report [label="Final Report", prompt="Synthesize the security, architecture, and code quality findings into a prioritized summary report with top 5 action items.", shape=tab]
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start -> fork
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fork -> security
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fork -> architecture
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fork -> quality
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security -> merge
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architecture -> merge
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quality -> merge
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merge -> report -> exit
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}
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```
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```bash
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fabro run files-internal/demo/06-parallel.fabro
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```
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## Fan-out with the fork node
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The `fork` node has `shape=component`, making it a **parallel fan-out node**. Every outgoing edge becomes a concurrent branch:
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```dot
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fork [label="Fork Analysis", shape=component, join_policy="wait_all", error_policy="continue"]
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fork -> security
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fork -> architecture
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fork -> quality
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```
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All three branches start at the same time. Each gets an isolated copy of the run context, so branches can't interfere with each other.
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### Join policies
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The `join_policy` controls when execution can proceed past the merge:
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| Policy | Behavior |
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|---|---|
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| `wait_all` | Wait for every branch to finish (default) |
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| `first_success` | Proceed as soon as one branch succeeds |
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| `k_of_n(N)` | Proceed after N branches succeed |
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| `quorum(0.5)` | Proceed after a fraction of branches succeed |
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### Error policies
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The `error_policy` controls what happens when a branch fails:
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| Policy | Behavior |
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|---|---|
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| `continue` | Run all branches even if some fail (default) |
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| `fail_fast` | Cancel remaining branches as soon as one fails |
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| `ignore` | Treat all branch failures as successes |
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This workflow uses `error_policy="continue"` so that a failure in one review perspective doesn't cancel the others.
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## Fan-in with the merge node
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The `merge` node has `shape=tripleoctagon`, making it a **merge (fan-in) node**. It collects results from all branches into a single context:
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```dot
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merge [label="Merge Findings", shape=tripleoctagon]
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security -> merge
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architecture -> merge
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quality -> merge
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```
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The merged branch results are available to downstream nodes. The `report` node receives all three perspectives in its preamble and synthesizes them.
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## Concurrency control
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By default, Fabro runs up to 4 parallel branches simultaneously. Control this with `max_parallel`:
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```dot
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fork [shape=component, max_parallel=2]
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```
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This is useful when branches are resource-intensive (e.g., each running a full agent session with tool calls) and you want to limit concurrency.
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## What you've learned
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- **Fan-out nodes** (`shape=component`) spawn concurrent branches
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- **Merge nodes** (`shape=tripleoctagon`) collect branch results
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- **Join policies** control when execution can proceed past the merge
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- **Error policies** control how branch failures are handled
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- Each branch gets an isolated copy of the context
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## Next
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<Card title="Multi-Model Routing" icon="arrow-right" href="/tutorials/multi-model">
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Assign different models to different workflow nodes using stylesheets.
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</Card>
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