feat: support complex structs in bridge via serde (#21)

[SAY-5]

Adds serde-based bridge support for complex Rust structs, letting the TypeScript side work with nested types, collections, and optional fields without manual conversion.

Also fixed UserProfile.id from u64 to u32 to avoid precision loss across the JS bridge (IEEE-754 doubles can't safely represent u64 values above 2^53-1).

Closes #21

[coderabbitai]

Walkthrough

Adds two new Serde-backed command handlers and data types to the Rust core, registers them in the command registry, extends TypeScript bridge types for those commands, and adds integration tests exercising nested-struct serialization, aggregation, and error cases.

Changes

Cohort / File(s)	Summary
Command Implementation crates/core/src/demo_commands.rs	Added Serde Serialize/Deserialize structs (GeoCoord, Address, UserProfile, ComputedFields, UserProfileEchoResponse, DataItem, AggregateResponse) and two commands: user_profile_echo (computes tag_count, avg_score) and data_aggregate (computes count, total, average, sorted/deduped categories). Added unit tests for both functions.
Registry Wiring crates/core/src/lib.rs	Imported demo_commands and registered demo_commands::user_profile_echo and demo_commands::data_aggregate in the command registry initialization via befu_macros::register_commands!.
Bridge Type Definitions packages/bridge/src/index.ts	Exported TypeScript interfaces mirroring the new Rust structs and extended BridgeCommandMap with 'user.profile.echo' and 'data.aggregate' entries for strongly-typed invocations.
Integration Tests crates/core/tests/bridge.rs	Added four Phase 6 tests: success round-trip for user.profile.echo (including computed fields), success and empty-input tests for data.aggregate, and a negative test asserting an INVALID_ARGUMENT error when a required nested field (coords) is missing.

Sequence Diagram

sequenceDiagram
    participant Client as TypeScript Client
    participant Bridge as Bridge Layer
    participant Serializer as Serde (JSON)
    participant Handler as Rust Command Handler

    Client->>Bridge: invoke('user.profile.echo', { profile: UserProfile })
    activate Bridge
    Bridge->>Serializer: parse JSON -> UserProfile
    activate Serializer
    Serializer-->>Bridge: UserProfile (nested structs)
    deactivate Serializer
    Bridge->>Handler: call user_profile_echo(profile)
    activate Handler
    Handler->>Handler: compute tag_count & avg_score
    Handler-->>Bridge: UserProfileEchoResponse
    deactivate Handler
    Bridge->>Serializer: serialize response -> JSON
    activate Serializer
    Serializer-->>Bridge: JSON result
    deactivate Serializer
    Bridge-->>Client: { ok: true, result: UserProfileEchoResponse }
    deactivate Bridge

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Possibly related PRs

• PR #16: Implements the befu_macros::register_commands! macro and #[command] procedural macros used to register the new command handlers.
• PR #15: Adds demo command patterns and registry wiring that this change extends with additional demo commands.

Poem

🐰
Hoppy structs hop through JSON lanes,
Nested tags and coords in trains,
Scores and counts all tallied bright,
Categories sorted, duplicates light,
A little rabbit cheers: bytes feel right!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title follows Conventional Commits style with 'feat:' prefix and clearly summarizes the main change: adding support for complex structs in the bridge via serde.
Linked Issues check	✅ Passed	The PR fully addresses all requirements from issue #21: extends befu::command macro for serde types, provides TypeScript interfaces in @befu/bridge, and includes comprehensive validation tests demonstrating complex nested structs and arrays.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to issue #21 requirements: new demo commands, TypeScript type definitions, and validation tests for complex struct bridging. A follow-up commit adjusting UserProfile.id (u64→u32) is also justified for JavaScript precision safety.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description check	✅ Passed	The PR description clearly relates to the changeset, explaining serde-based bridge support for complex structs and a u32/u64 fix for precision loss.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@crates/core/src/demo_commands.rs`:
- Around line 35-37: The UserProfile.id is a u64 which will lose precision when
mapped to a JS number; update serialization so IDs are sent as strings and
adjust the bridge typing accordingly: annotate UserProfile.id (the id field in
the UserProfile struct) with a serde serializer that emits/consumes a string
(e.g., #[serde(with = "serde_with::rust::display_fromstr")] or
#[serde(serialize_with = "...", deserialize_with = "...")]) and then change the
TypeScript interface in packages/bridge/src/index.ts to use id: string so
round-trips remain lossless. Ensure the chosen serde helper handles both
serialize and deserialize for u64-to-string conversion.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 9dc342db-31ce-43b0-88f5-461ba4d2d680

📥 Commits

Reviewing files that changed from the base of the PR and between 5febd64 and 33905ec.

📒 Files selected for processing (4)

• crates/core/src/demo_commands.rs
• crates/core/src/lib.rs
• crates/core/tests/bridge.rs
• packages/bridge/src/index.ts