⚡ Bolt: [performance improvement] Optimize dynamic SQL generation string formatting

[bashandbone]

💡 What:
Replaced intermediate Vec<String> accumulations and format! / .join(", ") calls with direct string generation using String::with_capacity and std::fmt::Write in build_upsert_stmt and build_delete_stmt within crates/flow/src/targets/d1.rs.

🎯 Why:
To construct dynamic SQL efficiently without triggering multiple O(n) heap allocations during string fragment generation. D1 adapter methods execute dynamically heavily and allocations impact end-to-end traversal/export time heavily.

📊 Impact:
Significantly reduces transient heap allocation counts, garbage collection sweeps, and memory copying overhead for every target synchronization query executed. Eliminates temporary memory arrays.

🔬 Measurement:
Ensure the tests from cargo test -p thread-flow --test d1_target_tests --test d1_minimal_tests pass successfully with zero performance regressions or feature changes.

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PR created automatically by Jules for task 5632950206202982987 started by @bashandbone

Summary by Sourcery

Optimize dynamic SQL generation and apply minor API and documentation cleanups across rule and AST components.

Enhancements:

• Streamline D1 upsert and delete SQL construction to avoid intermediate string allocations and reduce heap churn.
• Simplify rule-engine variable checking function signatures by removing unnecessary lifetime annotations.
• Tidy up string handling and formatting in AST engine and rule-engine utilities for improved clarity and consistency.

Documentation:

• Extend internal Bolt performance notes with guidance on efficient dynamic SQL string construction in database adapters.

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[sourcery-ai]

Reviewer's Guide

Optimizes dynamic SQL generation in the D1 export context to reduce allocations, performs minor signature cleanups in the rule-engine, and applies small style/formatting adjustments across a few modules, plus documents the performance pattern in the Bolt guide.

File-Level Changes

Change	Details	Files
Optimize INSERT/UPSERT SQL generation to avoid intermediate string allocations and vectors in D1ExportContext::build_upsert_stmt.	Replace Vec column/placeholder/update clause accumulation with direct writes into a preallocated String using String::with_capacity and std::fmt::Write. Pre-size params Vec based on key/value schema lengths to minimize reallocations. Manually generate the VALUES placeholder list and ON CONFLICT UPDATE clause using in-place string concatenation and simple boolean flags for comma handling.	crates/flow/src/targets/d1.rs
Optimize DELETE SQL generation in D1ExportContext::build_delete_stmt to build the WHERE clause directly into a preallocated String.	Replace where_clauses Vec and format!/join pattern with a single String::with_capacity and write!-based appends. Use a boolean flag to handle "AND" separator insertion while iterating key fields. Pre-size the params Vec based on key_fields_schema length.	crates/flow/src/targets/d1.rs
Simplify lifetimes in rule-engine variable checking helpers by using non-lifetime-borrowed references for constraints and transform parameters.	Update function signatures in check_var.rs to accept &RapidMap and &Option without explicit lifetime parameters. Propagate signature changes through helper functions check_vars_in_rewriter, check_vars, check_var_in_constraints, and check_var_in_transform.	crates/rule-engine/src/check_var.rs
Apply small readability and style cleanups in several modules.	Reformat a from_utf8 unwrap_or_else call onto a single line in tree_sitter::ContentExt implementation. Expand a test assert_eq! over multiple lines for clarity in tree-sitter tests. Format the Rule::Pattern defined_vars() mapping chain across multiple lines for readability. Inline a referent_rule::Registration::read() lock unwrap chain into a single line.	crates/ast-engine/src/tree_sitter/mod.rs crates/rule-engine/src/rule/mod.rs crates/rule-engine/src/rule/referent_rule.rs
Document the dynamic SQL string-generation performance pattern in the Bolt engineering notes.	Add a new section describing why Vec + format!/join is inefficient for highly called SQL generators. Recommend using String::with_capacity and write!-based appends for dynamic string building in performance-critical paths.	.jules/bolt.md

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