⚡ Bolt: [performance improvement] Optimize D1 target SQL statement building

[bashandbone]

💡 What
Refactored build_upsert_stmt and build_delete_stmt in crates/flow/src/targets/d1.rs to construct dynamic SQL queries directly into pre-allocated String buffers using std::fmt::Write. This replaces the previous pattern of collecting query parts into intermediate vectors (vec![]) and using format! with .join(). Query parameter vectors are also now pre-allocated with exact capacities.

🎯 Why
The previous implementation performed multiple heap allocations per query to create intermediate strings and vectors, causing unnecessary memory churn on a hot path during data export to Cloudflare D1 targets.

📊 Impact
Significantly reduces heap allocations and string copying overhead per generated SQL query, which improves memory efficiency and query generation throughput during bulk data exports.

🔬 Measurement
Verify the optimizations by running cargo test -p thread-flow --test d1_target_tests --test d1_minimal_tests to ensure that identical, correct SQL queries are still being generated under the new, faster implementation.

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PR created automatically by Jules for task 10239718748718497456 started by @bashandbone

Summary by Sourcery

Optimize SQL statement construction for D1 exports and perform minor API and formatting cleanups across supporting crates.

Enhancements:

• Build D1 upsert and delete SQL statements directly into pre-allocated string buffers while pre-sizing parameter vectors to reduce allocations on a hot path.
• Simplify lifetime usage in variable checking helpers by removing unnecessary explicit lifetimes from function signatures.
• Tidy up string and assertion formatting for improved readability in AST and rule engine modules.

Documentation:

• Add a Bolt engineering note documenting the performance pattern of direct string formatting for dynamic SQL query construction.

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[sourcery-ai]

Reviewer's Guide

Optimizes SQL statement construction for D1 exports by building queries directly into preallocated String buffers and parameter vectors, plus a few minor API-signature and formatting cleanups elsewhere in the codebase.

File-Level Changes

Change	Details	Files
Optimize D1 upsert SQL statement construction to avoid intermediate allocations.	Replace intermediate column, placeholder, and update-clause vectors with direct writes into a preallocated SQL String using std::fmt::Write. Preallocate the params Vec based on key and value schema lengths to avoid repeated reallocations. Build the VALUES placeholder list and ON CONFLICT update-clause list directly from the accumulated params and value_fields_schema, maintaining original query semantics.	crates/flow/src/targets/d1.rs
Optimize D1 delete SQL statement construction to build the WHERE clause directly into a String buffer.	Replace collection of where_clauses strings with direct writes into a preallocated SQL String using std::fmt::Write. Preallocate the params Vec to the number of key fields. Maintain logical conjunction of key-field predicates while reducing temporary allocations.	crates/flow/src/targets/d1.rs
Minor cleanup of string UTF-8 recovery and test formatting in the AST engine.	Refactor a from_utf8 unwrap_or_else call into a single line without changing behavior. Reformat a multi-line assert_eq! for clarity while keeping the test logic identical.	crates/ast-engine/src/tree_sitter/mod.rs
Simplify lifetimes in rule-engine helper functions and slightly tidy registration reads.	Remove unused explicit lifetime parameters from check_var_in_constraints and check_var_in_transform and take references directly, simplifying signatures. Keep behavior identical while improving readability of the Registration::read method’s unwrap_or_else call. Reformat Rule::Pattern defined_vars mapping into a multi-line chain for clarity.	crates/rule-engine/src/check_var.rs crates/rule-engine/src/rule/mod.rs crates/rule-engine/src/rule/referent_rule.rs
Document the new performance pattern for SQL query building in the Bolt notes.	Add a Bolt log entry describing the motivation and pattern for direct String formatting and exact-capacity Vec allocations when building dynamic SQL queries.	.jules/bolt.md

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[sourcery-ai]

Hey - I've left some high level feedback:

• In both build_upsert_stmt and build_delete_stmt, you repeatedly use use std::fmt::Write; let _ = write!(...); since String writes are infallible, consider either pulling the import to the module level and using write! directly (without let _ =) or adding a small helper to avoid the repeated boilerplate.
• The String::with_capacity calls in the D1 SQL builders use fairly opaque constants (e.g., 128, 64, and per-field multipliers); adding a brief comment explaining how these were chosen or tying them to typical query shapes would make future maintenance and tuning easier.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In both `build_upsert_stmt` and `build_delete_stmt`, you repeatedly use `use std::fmt::Write; let _ = write!(...)`; since `String` writes are infallible, consider either pulling the import to the module level and using `write!` directly (without `let _ =`) or adding a small helper to avoid the repeated boilerplate.
- The `String::with_capacity` calls in the D1 SQL builders use fairly opaque constants (e.g., `128`, `64`, and per-field multipliers); adding a brief comment explaining how these were chosen or tying them to typical query shapes would make future maintenance and tuning easier.

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[Copilot]

Pull request overview

Refactors D1 SQL statement generation in thread-flow to reduce heap allocations on a hot path by building SQL directly into pre-allocated String buffers and pre-sizing parameter vectors.

Changes:

• Optimized build_upsert_stmt / build_delete_stmt in crates/flow/src/targets/d1.rs to avoid intermediate Vec<String>/format! allocations.
• Minor formatting-only refactors across rule-engine and ast-engine modules.
• Added a new performance “learning/action” entry to .jules/bolt.md.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
crates/flow/src/targets/d1.rs	Builds INSERT/DELETE SQL directly into pre-allocated buffers; pre-allocates params vec capacity.
crates/rule-engine/src/rule/referent_rule.rs	Formatting-only refactor of a read-lock chain.
crates/rule-engine/src/rule/mod.rs	Formatting-only refactor for defined_vars chain readability.
crates/rule-engine/src/check_var.rs	Removes unnecessary explicit lifetimes in helper functions.
crates/ast-engine/src/tree_sitter/mod.rs	Formatting-only refactors in string splice and a test assert.
.jules/bolt.md	Adds a new entry describing the SQL string-building optimization.

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