⚡ Bolt: [performance improvement] optimize pathbuf allocations in tarjan SCC algorithm

[bashandbone]

💡 What: Optimized to_path_buf() allocations in the tarjan_dfs graph traversal function for strongly connected components inside thread-flow's invalidation system.
🎯 Why: In TarjanState during graph traversal for finding cycles, calling .to_path_buf() on borrowed &Path values repeatedly within loops to query HashSets and HashMaps led to unnecessary O(E) heap allocations.
📊 Impact: Reduces memory allocation churn significantly during large invalidation graph cycle detections by changing lookup complexity from allocating to pure read.
🔬 Measurement: Verify by running cargo test -p thread-flow --test invalidation_tests ensuring no regressions, and note the avoidance of O(Edges) string allocations. Also clippy no longer emits explicit lifetime warnings in check_var.rs.

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PR created automatically by Jules for task 3281374725584587497 started by @bashandbone

Summary by Sourcery

Optimize path-based lookups in the Tarjan SCC invalidation traversal to avoid redundant allocations and clean up related rule-engine lifetimes.

Enhancements:

• Use borrowed path references instead of creating new PathBuf allocations for TarjanState map and set lookups in the invalidation graph traversal.
• Simplify function signatures in the rule-engine variable checking helpers by removing unnecessary explicit lifetimes and using shared references directly.
• Document the performance lesson about avoiding redundant to_path_buf and clone calls in Tarjan-style graph algorithms in the Bolt notes.

Documentation:

• Extend the Bolt performance notes with guidance on avoiding redundant to_path_buf calls and unnecessary allocations in Tarjan SCC and graph traversals.

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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Optimizes Tarjan SCC traversal by eliminating repeated PathBuf allocations in map/set lookups and simplifies some rule-engine APIs by removing unnecessary lifetimes, plus updates the Bolt playbook documentation with the new performance lesson.

Class diagram for optimized TarjanState SCC path lookups

classDiagram
    class InvalidationDetector {
        +tarjan_dfs(v: &Path, state: &mut TarjanState)
    }

    class TarjanState {
        +indices: HashMap~PathBuf, usize~
        +lowlinks: HashMap~PathBuf, usize~
        +on_stack: HashSet~PathBuf~
        +stack: Vec~PathBuf~
        +get_index(v: &Path) usize
        +get_lowlink(v: &Path) usize
        +get_lowlink_mut(v: &Path) &mut usize
        +is_on_stack(v: &Path) bool
    }

    InvalidationDetector --> TarjanState : uses

    class Path {
    }

    class PathBuf {
    }

    TarjanState ..> Path : borrowed_lookup_keys
    TarjanState ..> PathBuf : owned_storage_keys

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Class diagram for simplified check_var helper APIs

classDiagram
    class RuleEngineCheckVarModule {
        +get_vars_from_rules(rule: &Rule, utils: &RuleRegistration) RapidSetString
        +check_var_in_constraints(vars: RapidSetString, constraints: &RapidMapMetaVarRule) RResultRapidSetString
        +check_var_in_transform(vars: RapidSetString, transform: &OptionTransform) RResultRapidSetString
    }

    class Rule {
        +defined_vars() RapidSetString
        +used_vars() RapidSetString
    }

    class RuleRegistration {
    }

    class RapidSetString {
    }

    class RapidMapMetaVarRule {
    }

    class OptionTransform {
    }

    class Transform {
    }

    class RResultRapidSetString {
    }

    RuleEngineCheckVarModule --> Rule : reads
    RuleEngineCheckVarModule --> RuleRegistration : reads
    RuleEngineCheckVarModule --> RapidSetString : moves_ownership
    RuleEngineCheckVarModule --> RapidMapMetaVarRule : borrows_constraints
    RuleEngineCheckVarModule --> OptionTransform : borrows_transform
    OptionTransform --> Transform : wraps
    Rule --> RapidSetString : returns_sets
    RuleEngineCheckVarModule --> RResultRapidSetString : returns

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Flow diagram for optimized PathBuf allocation in Tarjan SCC lookups

flowchart TD
    A["Start tarjan_dfs with v: &Path"] --> B["Lookup v in indices using &Path"]
    B --> C{"Index for v exists?"}
    C -->|"Yes"| D["Lookup v in lowlinks using &Path"]
    C -->|"No"| E["Allocate PathBuf from v and insert into indices and lowlinks"]
    E --> F["Push owned PathBuf onto stack and mark on_stack"]
    D --> G["Process dependencies using borrowed dep: &Path"]
    G --> H["Use dep directly in indices, lowlinks, on_stack lookups"]
    H --> I{"SCC root detected?"}
    I -->|"Yes"| J["Pop PathBuf nodes from stack to form SCC"]
    I -->|"No"| K["Continue DFS traversal"]
    J --> L["End traversal for v"]
    K --> L

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File-Level Changes

Change	Details	Files
Avoid repeated PathBuf allocations in Tarjan SCC state lookups during invalidation graph traversal.	Replace HashMap/HashSet lookups that used v.to_path_buf() with lookups that use the borrowed &Path directly for indices and lowlinks. Ensure lowlink and index retrieval and mutation operate on borrowed keys to avoid per-edge heap allocations while preserving algorithm semantics.	crates/flow/src/incremental/invalidation.rs
Simplify rule-engine function signatures by removing unnecessary explicit lifetimes from constraint and transform helpers.	Drop explicit lifetime parameter from check_var_in_constraints and accept a shared reference to RapidMap instead. Drop explicit lifetime parameter from check_var_in_transform and accept a shared reference to Option instead, keeping behavior unchanged.	crates/rule-engine/src/check_var.rs
Extend Bolt performance notes with guidance on avoiding redundant PathBuf and clone allocations in graph algorithms.	Document the cost of repeated to_path_buf calls in TarjanState map/set operations and the benefit of using borrowed keys instead. Add a general recommendation to avoid allocations when performing membership checks in RapidSet/RapidMap and only allocate on insertion/ownership transfer.	.jules/bolt.md

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[Copilot]

Pull request overview

Optimizes parts of the invalidation cycle-detection path (Tarjan SCC) by removing unnecessary PathBuf allocations during map/set lookups, and cleans up an unrelated clippy-driven lifetime signature issue.

Changes:

• Use borrowed &Path keys directly for RapidMap<PathBuf, _> lookups inside tarjan_dfs, eliminating repeated to_path_buf() heap allocations on hot paths.
• Remove redundant explicit lifetimes from helper functions in check_var.rs to satisfy clippy and simplify signatures.
• Document the performance learning in .jules/bolt.md.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
crates/rule-engine/src/check_var.rs	Simplifies helper signatures by removing unnecessary lifetime parameters.
crates/flow/src/incremental/invalidation.rs	Avoids to_path_buf() allocations in Tarjan SCC lookups by using borrowed &Path keys.
.jules/bolt.md	Adds a note describing the performance rationale and recommended practice.

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