⚡ Bolt: [performance improvement] optimize path allocations in incremental invalidation

[bashandbone]

💡 What: Removed &v.to_path_buf() calls in crates/flow/src/incremental/invalidation.rs map queries (get_mut and get), using borrowed v instead. Cleaned up explicit lifetime lint warnings in check_var.rs along the way.
🎯 Why: &v.to_path_buf() allocates a new string-backed Path on the heap. Doing this inside Tarjan's strongly-connected-components inner loop (graph edges) resulted in O(E) memory churn per graph connected component calculation. Borrowing allows us to look up references instantly in RapidMap without allocations.
📊 Impact: Faster invalidation propagation algorithms with lower peak memory footprint on deeply-connected component graphs.
🔬 Measurement: Verified via memory correctness traces (test_get.rs checks) and cargo test -p thread-flow --test invalidation_tests. All SCC, topological, and tree validation checks passed successfully.

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PR created automatically by Jules for task 968163309968730354 started by @bashandbone

Summary by Sourcery

Optimize incremental invalidation graph traversal to reduce path allocation overhead and clean up lifetime usage in variable checking utilities.

Enhancements:

• Reuse borrowed Path references in Tarjan SCC indices/lowlink maps to avoid repeated PathBuf allocations during invalidation traversal.
• Simplify function signatures in variable constraint/transform checks by removing unnecessary explicit lifetimes and using reference types directly.

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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Optimizes incremental invalidation SCC traversal by using borrowed path references instead of heap-allocating PathBufs on every map access, and cleans up unnecessary explicit lifetimes in rule-engine variable checking helpers.

Sequence diagram for optimized SCC traversal map lookups in incremental invalidation

sequenceDiagram
    participant InvalidationDetector
    participant TarjanState
    participant LowlinksMap as RapidMap_lowlinks
    participant IndicesMap as RapidMap_indices
    participant OnStackSet as RapidSet_on_stack
    participant V as Path_v
    participant Dep as Path_dep

    InvalidationDetector->>TarjanState: tarjan_visit(V)
    loop for_each_dependency_of_v
        InvalidationDetector->>TarjanState: next dependency -> Dep
        alt dep_not_visited
            InvalidationDetector->>TarjanState: recurse tarjan_visit(Dep)
            TarjanState->>LowlinksMap: get(Dep)
            LowlinksMap-->>TarjanState: w_lowlink
            Note over TarjanState,LowlinksMap: Before: get_mut(&v.to_path_buf())
            TarjanState->>LowlinksMap: get_mut(V)
            LowlinksMap-->>TarjanState: v_lowlink_ref
            TarjanState->>TarjanState: *v_lowlink_ref = min(*v_lowlink_ref, w_lowlink)
        else dep_on_stack
            TarjanState->>OnStackSet: contains(Dep)
            OnStackSet-->>TarjanState: true
            TarjanState->>IndicesMap: get(Dep)
            IndicesMap-->>TarjanState: w_index
            Note over TarjanState,LowlinksMap: Before: get_mut(&v.to_path_buf())
            TarjanState->>LowlinksMap: get_mut(V)
            LowlinksMap-->>TarjanState: v_lowlink_ref
            TarjanState->>TarjanState: *v_lowlink_ref = min(*v_lowlink_ref, w_index)
        end
    end

    Note over TarjanState,IndicesMap: Before: get(&v.to_path_buf())
    TarjanState->>IndicesMap: get(V)
    IndicesMap-->>TarjanState: v_index

    Note over TarjanState,LowlinksMap: Before: get(&v.to_path_buf())
    TarjanState->>LowlinksMap: get(V)
    LowlinksMap-->>TarjanState: v_lowlink

    TarjanState->>TarjanState: if v_lowlink == v_index then form_SCC()
    TarjanState-->>InvalidationDetector: SCC for V

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Class diagram for updated invalidation and rule-engine helper APIs

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

    class TarjanState {
        +indices: RapidMap~Path, usize~
        +lowlinks: RapidMap~Path, usize~
        +on_stack: RapidSet~Path~
        +stack: Vec~Path~
    }

    InvalidationDetector --> TarjanState: uses

    class CheckVarModule {
        +get_vars_from_rules(rule: &Rule, utils: &RuleRegistration) RapidSet~String~
        +check_var_in_constraints(vars: RapidSet~String~, constraints: &RapidMap~MetaVariableID, Rule~) RResult~RapidSet~String~~
        +check_var_in_transform(vars: RapidSet~String~, transform: &Option~Transform~) RResult~RapidSet~String~~
    }

    class Rule {
        +defined_vars() Iterator~String~
        +meta_vars() Iterator~String~
    }

    class RuleRegistration {
        +constraints: RapidMap~MetaVariableID, Rule~
        +transform: Option~Transform~
    }

    class RapidMap~K, V~ {
    }

    class RapidSet~T~ {
    }

    class Transform {
    }

    class MetaVariableID {
    }

    class RResult~T~ {
    }

    CheckVarModule --> Rule: reads
    CheckVarModule --> RuleRegistration: reads
    CheckVarModule --> RapidMap: uses
    CheckVarModule --> RapidSet: uses
    CheckVarModule --> Transform: uses
    CheckVarModule --> MetaVariableID: uses
    CheckVarModule --> RResult: returns

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File-Level Changes

Change	Details	Files
Avoid heap allocations during SCC traversal in incremental invalidation by using borrowed Path keys in RapidMap lookups.	Replace lowlink map lookups using &v.to_path_buf() with lookups directly on borrowed &Path values in Tarjan SCC recursion. Replace index map lookups using &v.to_path_buf() with lookups directly on borrowed &Path values. Add explanatory comments documenting that the change avoids O(E) heap allocations inside the SCC traversal loop.	crates/flow/src/incremental/invalidation.rs
Simplify function signatures by removing unnecessary explicit lifetimes in rule-engine variable/constraint helpers.	Remove explicit lifetime parameter from check_var_in_constraints and accept &RapidMap instead of a lifetime-annotated reference. Remove explicit lifetime parameter from check_var_in_transform and accept &Option instead of a lifetime-annotated reference. Rely on elided lifetimes for function signatures to address explicit lifetime lint warnings.	crates/rule-engine/src/check_var.rs

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[sourcery-ai]

Hey - I've left some high level feedback:

• In the Tarjan loop you repeatedly call state.lowlinks.get_mut(v) in both branches; consider factoring this lookup so v_lowlink is obtained once per iteration (or once per v) to reduce RapidMap lookups in this hot path.
• The new // Bolt: ... comments are quite tool-specific; consider rephrasing them in neutral terms (e.g., just explaining the allocation avoidance) to keep the codebase free of vendor- or tool-branded annotations.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In the Tarjan loop you repeatedly call `state.lowlinks.get_mut(v)` in both branches; consider factoring this lookup so `v_lowlink` is obtained once per iteration (or once per `v`) to reduce RapidMap lookups in this hot path.
- The new `// Bolt: ...` comments are quite tool-specific; consider rephrasing them in neutral terms (e.g., just explaining the allocation avoidance) to keep the codebase free of vendor- or tool-branded annotations.

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[Copilot]

Pull request overview

This PR reduces heap allocations during incremental invalidation’s Tarjan SCC traversal by switching RapidMap lookups from &v.to_path_buf() (allocating) to borrowed &Path lookups, leveraging PathBuf: Borrow<Path> support in the underlying hash map. It also simplifies a couple of helper function signatures in the rule-engine to remove unnecessary explicit lifetimes.

Changes:

• Avoids per-edge PathBuf allocations in Tarjan’s algorithm by using borrowed &Path for RapidMap::get(_mut) queries.
• Removes explicit lifetimes from two internal helper functions in check_var.rs (constraints/transform checks).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
crates/rule-engine/src/check_var.rs	Removes unnecessary explicit lifetimes in helper function signatures.
crates/flow/src/incremental/invalidation.rs	Replaces allocating to_path_buf() map lookups with borrowed &Path lookups in Tarjan SCC traversal.

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