Serialization builds an intermediate owned JSON tree

Timing: Follow-up after trial/3 merges into main; defer implementation until then.

Review baseline: Local trial/3 at a094418baf6388e3eeca23821df481a7f0a8751c. This branch is not yet on the remote. Source locations below refer to that snapshot and should be rechecked after merge.

Problem

Value::serialize converts into a complete owned serde_json::Value before invoking the requested serializer, copying JSON-compatible strings and containers. Nest::path_as similarly constructs owned JSON before typed deserialization. These paths can impose avoidable traversal and allocation costs; they are not established correctness failures.

Evidence

crates/lib/src/data/value.rs:632-639: self.to_json()?.serialize(serializer).
crates/lib/src/data/nest.rs:417-425: rich value → owned JSON → typed value.

Acceptance criteria

Review direct Serde serialization/deserialization adapters to avoid unnecessary intermediate trees where practical.
Preserve finite budgets, nested-path diagnostics, insertion order, missing/null semantics, and explicit rejection of unsupported native/date/byte/file values.
Preserve the current prevalidation/error contract; do not silently change partial-output behavior.
Verify wire compatibility and error paths, and document allocation/performance evidence for the selected approach.

Code examples and suggested direction

Current allocation path:

self.to_json()
    .map_err(serde::ser::Error::custom)?
    .serialize(serializer)

Suggested shape, using new private helpers that still need implementation:

// Check budgets AND JSON-compatible variants before the serializer writes.
preflight_json(self, &ParseLimits::default())
    .map_err(serde::ser::Error::custom)?;

// Borrow the validated tree instead of building an owned JSON copy.
// CheckedJson recursively serializes children without repeating preflight.
CheckedJson(self).serialize(serializer)

Checking budgets alone is insufficient: an unsupported nested native value must also be detected before output begins, matching the current conversion-before-serialization behavior.

Suggested investigation and fix notes

Deferred until trial/3 is merged into main. Recheck the merged source and tests first. The snippets are examples/proposals, not an approved patch or a change to frozen contracts.

Separate validation from representation. Inspect Value::measure, json_at, Serialize for Value, Serialize for Nest, and Nest::path_as. Preserve default versus caller-selected limits at each entry point.
Implement a private borrowed serializer wrapper after a complete JSON-compatibility/budget preflight. Use serialize_seq/serialize_map and borrow strings/keys. Recursive calls should serialize already-checked children instead of revalidating every subtree.
Keep the current diagnostic paths, integer/number representation, insertion order, and unsupported-variant policy. Do not silently switch to externally tagged enum serialization through a derive.
Treat typed deserialization as a separate, optional phase. A custom borrowed deserializer must retain DeserializeOwned behavior and equivalent type errors; leave it for a follow-up if that adds disproportionate complexity.
Compare allocation counts or peak allocations for nested realistic data before/after. A second validation traversal may remain justified even when the owned intermediate tree is removed.

Behavior example using current APIs:

use stackpress_lib::{Result, Value};

fn wire_example() -> Result<()> {
    let value = Value::try_from(serde_json::json!({
        "id": 7, "active": false, "optional": null
    }))?;
    assert_eq!(
        serde_json::to_string(&value)?,
        r#"{"id":7,"active":false,"optional":null}"#
    );
    assert!(serde_json::to_string(&Value::Bytes(vec![1, 2])).is_err());
    Ok(())
}

Extend data_contracts and request_response_contracts, including a custom serializer proving preflight failures do not begin output. Start with cargo test -p stackpress-lib --locked. Reference: implementing Serialize.

Implementation workflow: After the merge, follow .agents/workflows/rust-programming.md: prove the affected behavior, complete the three test-verified review rounds, and record relevant formatting/lints/docs, feature/platform scope, and applicable development coverage. Preserve unrelated changes.

Fixed on trial/3 in 644795f (merged as 64a5b70, task 00010 lane 1; not yet on main, so leaving open).

Value/Nest serialization and Nest::path_as now borrow through one private checked JSON view instead of building an owned serde_json::Value tree.
Budget validation and JSON-compatibility preflight both still run before any serializer/visitor call, with the original error precedence and path diagnostics (an empty-key path regression was caught and fixed during review).
Allocation evidence is recorded in the task receipt.

Coordinator-verified: fmt, Clippy -D warnings, Rustdoc -D warnings, cargo +1.96.0 check, 454 workspace tests, 856 doctests pass; lib production coverage 93.64%.

Fix owner review issues #11, #1, #2, #5 and lib parts of #4, #7 (task…

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Serialization builds an intermediate owned JSON tree #2

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Serialization builds an intermediate owned JSON tree #2

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cblanquera commented on Oct 26, 2026

Suggested investigation and fix notes

cblanquera commented on Oct 26, 2026

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