core: cut codex-core compile time 63% with native async ToolHandler (openai#16630)

## Why

`ToolHandler` was still paying a large compile-time tax from
`#[async_trait]` on every concrete handler impl, even though the only
object-safe boundary the registry actually stores is the internal
`AnyToolHandler` adapter.

This PR removes that macro-generated async wrapper layer from concrete
`ToolHandler` impls while keeping the existing object-safe shim in
`AnyToolHandler`. In practice, that gets essentially the same
compile-time win as the larger type-erasure refactor in openai#16627, but with
a much smaller diff and without changing the public shape of
`ToolHandler<Output = T>`.

That tradeoff matters here because this is a broad `codex-core` hotspot
and reviewers should be able to judge the compile-time impact from hard
numbers, not vibes.

## Headline result

On a clean `codex-core` package rebuild (`cargo clean -p codex-core`
before each command), rustc `total` dropped from **187.15s to 68.98s**
versus the shared `0bd31dc382bd` baseline: **-63.1%**.

The biggest hot passes dropped by roughly **71-72%**:

| Metric | Baseline `0bd31dc382bd` | This PR `41f7ac0adeac` | Delta |
|---|---:|---:|---:|
| `total` | 187.15s | 68.98s | **-63.1%** |
| `generate_crate_metadata` | 84.53s | 24.49s | **-71.0%** |
| `MIR_borrow_checking` | 84.13s | 24.58s | **-70.8%** |
| `monomorphization_collector_graph_walk` | 79.74s | 22.19s | **-72.2%**
|
| `evaluate_obligation` self-time | 180.62s | 46.91s | **-74.0%** |

Important caveat: `-Z time-passes` timings are nested, so
`generate_crate_metadata` and `monomorphization_collector_graph_walk`
are mostly overlapping, not additive.

## Why this PR over openai#16627

openai#16627 already proved that the `ToolHandler` stack was the right
hotspot, but it got there by making `ToolHandler` object-safe and
changing every handler to return `BoxFuture<Result<AnyToolResult, _>>`
directly.

This PR keeps the lower-churn shape:

- `ToolHandler` remains generic over `type Output`.
- Concrete handlers use native RPITIT futures with explicit `Send`
bounds.
- `AnyToolHandler` remains the only object-safe adapter and still does
the boxing at the registry boundary, as before.
- The implementation diff is only **33 files, +28/-77**.

The measurements are at least comparable, and in this run this PR is
slightly faster than openai#16627 on the pass-level total:

| Metric | openai#16627 | This PR | Delta |
|---|---:|---:|---:|
| `total` | 79.90s | 68.98s | **-13.7%** |
| `generate_crate_metadata` | 25.88s | 24.49s | **-5.4%** |
| `monomorphization_collector_graph_walk` | 23.54s | 22.19s | **-5.7%**
|
| `evaluate_obligation` self-time | 43.29s | 46.91s | +8.4% |

## Profile data

### Crate-level timings

`cargo +nightly build -p codex-core --lib -Z unstable-options
--timings=json` after `cargo clean -p codex-core`.

Baseline data below is reused from the shared parent `0bd31dc382bd`
profile because this PR and openai#16627 are both one commit on top of that
same parent.

| Crate | Baseline `duration` | This PR `duration` | Delta | Baseline
`rmeta_time` | This PR `rmeta_time` | Delta |
|---|---:|---:|---:|---:|---:|---:|
| `codex_core` | 187.380776583s | 69.171113833s | **-63.1%** |
174.474507208s | 55.873015583s | **-68.0%** |
| `starlark` | 17.90s | 16.773824125s | -6.3% | n/a | 8.8999965s | n/a |

### Pass-level timings

`cargo +nightly rustc -p codex-core --lib -- -Z time-passes -Z
time-passes-format=json` after `cargo clean -p codex-core`.

| Pass | Baseline | This PR | Delta |
|---|---:|---:|---:|
| `total` | 187.150662083s | 68.978770375s | **-63.1%** |
| `generate_crate_metadata` | 84.531864625s | 24.487462958s | **-71.0%**
|
| `MIR_borrow_checking` | 84.131389375s | 24.575553875s | **-70.8%** |
| `monomorphization_collector_graph_walk` | 79.737515042s |
22.190207417s | **-72.2%** |
| `codegen_crate` | 12.362532292s | 12.695237625s | +2.7% |
| `type_check_crate` | 4.4765405s | 5.442019542s | +21.6% |
| `coherence_checking` | 3.311121208s | 4.239935292s | +28.0% |
| process `real` / `user` / `sys` | 187.70s / 201.87s / 4.99s | 69.52s /
85.90s / 2.92s | n/a |

### Self-profile query summary

`cargo +nightly rustc -p codex-core --lib -- -Z self-profile=... -Z
self-profile-events=default,query-keys,args,llvm,artifact-sizes` after
`cargo clean -p codex-core`, summarized with `measureme summarize -p
0.5`.

| Query / phase | Baseline self time | This PR self time | Delta |
Baseline total time | This PR total time | Baseline item count | This PR
item count | Baseline cache hits | This PR cache hits |
|---|---:|---:|---:|---:|---:|---:|---:|---:|---:|
| `evaluate_obligation` | 180.62s | 46.91s | **-74.0%** | 182.08s |
48.37s | 572,234 | 388,659 | 1,130,998 | 1,058,553 |
| `mir_borrowck` | 1.42s | 1.49s | +4.9% | 93.77s | 29.59s | n/a | 6,184
| n/a | 15,298 |
| `typeck` | 1.84s | 1.87s | +1.6% | 2.38s | 2.44s | n/a | 9,367 | n/a |
79,247 |
| `LLVM_module_codegen_emit_obj` | n/a | 17.12s | n/a | 17.01s | 17.12s
| n/a | 256 | n/a | 0 |
| `LLVM_passes` | n/a | 13.07s | n/a | 12.95s | 13.07s | n/a | 1 | n/a |
0 |
| `codegen_module` | n/a | 12.33s | n/a | 12.22s | 13.64s | n/a | 256 |
n/a | 0 |
| `items_of_instance` | n/a | 676.00ms | n/a | n/a | 24.96s | n/a |
99,990 | n/a | 0 |
| `type_op_prove_predicate` | n/a | 660.79ms | n/a | n/a | 24.78s | n/a
| 78,762 | n/a | 235,877 |

| Summary | Baseline | This PR |
|---|---:|---:|
| `evaluate_obligation` % of total CPU | 70.821% | 38.880% |
| self-profile total CPU time | 255.042999997s | 120.661175956s |
| process `real` / `user` / `sys` | 220.96s / 235.02s / 7.09s | 86.35s /
103.66s / 3.54s |

### Artifact sizes

From the same `measureme summarize` output:

| Artifact | Baseline | This PR | Delta |
|---|---:|---:|---:|
| `crate_metadata` | 26,534,471 bytes | 26,545,248 bytes | +10,777 |
| `dep_graph` | 253,181,425 bytes | 239,240,806 bytes | -13,940,619 |
| `linked_artifact` | 565,366,624 bytes | 562,673,176 bytes | -2,693,448
|
| `object_file` | 513,127,264 bytes | 510,464,096 bytes | -2,663,168 |
| `query_cache` | 137,440,945 bytes | 136,982,566 bytes | -458,379 |
| `cgu_instructions` | 3,586,307 bytes | 3,575,121 bytes | -11,186 |
| `codegen_unit_size_estimate` | 2,084,846 bytes | 2,078,773 bytes |
-6,073 |
| `work_product_index` | 19,565 bytes | 19,565 bytes | 0 |

### Baseline hotspots before this change

These are the top normalized obligation buckets from the shared baseline
profile:

| Obligation bucket | Samples | Duration |
|---|---:|---:|
| `outlives:tasks::review::ReviewTask` | 1,067 | 6.33s |
| `outlives:tools::handlers::unified_exec::UnifiedExecHandler` | 896 |
5.63s |
| `trait:T as tools::registry::ToolHandler` | 876 | 5.45s |
| `outlives:tools::handlers::shell::ShellHandler` | 888 | 5.37s |
| `outlives:tools::handlers::shell::ShellCommandHandler` | 870 | 5.29s |
|
`outlives:tools::runtimes::shell::unix_escalation::CoreShellActionProvider`
| 637 | 3.73s |
| `outlives:tools::handlers::mcp::McpHandler` | 695 | 3.61s |
| `outlives:tasks::regular::RegularTask` | 726 | 3.57s |

Top `items_of_instance` entries before this change were mostly concrete
async handler/task impls:

| Instance | Duration |
|---|---:|
| `tasks::regular::{impl#2}::run` | 3.79s |
| `tools::handlers::mcp::{impl#0}::handle` | 3.27s |
| `tools::runtimes::shell::unix_escalation::{impl#2}::determine_action`
| 3.09s |
| `tools::handlers::agent_jobs::{impl#11}::handle` | 3.07s |
| `tools::handlers::multi_agents::spawn::{impl#1}::handle` | 2.84s |
| `tasks::review::{impl#4}::run` | 2.82s |
| `tools::handlers::multi_agents_v2::spawn::{impl#2}::handle` | 2.80s |
| `tools::handlers::multi_agents::resume_agent::{impl#1}::handle` |
2.73s |
| `tools::handlers::unified_exec::{impl#2}::handle` | 2.54s |
| `tasks::compact::{impl#4}::run` | 2.45s |

## What changed

Relevant pre-change registry shape:
[`codex-rs/core/src/tools/registry.rs`](https://github.com/openai/codex/blob/0bd31dc382bd1c33dc2bb6b97069c76aa10ba14b/codex-rs/core/src/tools/registry.rs#L38-L219)

Current registry shape in this PR:
[`codex-rs/core/src/tools/registry.rs`](https://github.com/openai/codex/blob/41f7ac0adeac81d667541853d6546267d6083613/codex-rs/core/src/tools/registry.rs#L38-L203)

- `ToolHandler::{is_mutating, handle}` now return native `impl Future +
Send` futures instead of using `#[async_trait]`.
- `AnyToolHandler` remains the object-safe adapter and boxes those
futures at the registry boundary with explicit lifetimes.
- Concrete handlers and the registry test handler drop `#[async_trait]`
but otherwise keep their async method bodies intact.
- Representative examples:
[`codex-rs/core/src/tools/handlers/shell.rs`](https://github.com/openai/codex/blob/41f7ac0adeac81d667541853d6546267d6083613/codex-rs/core/src/tools/handlers/shell.rs#L223-L379),
[`codex-rs/core/src/tools/handlers/unified_exec.rs`](https://github.com/openai/codex/blob/41f7ac0adeac81d667541853d6546267d6083613/codex-rs/core/src/tools/handlers/unified_exec.rs),
[`codex-rs/core/src/tools/registry_tests.rs`](https://github.com/openai/codex/blob/41f7ac0adeac81d667541853d6546267d6083613/codex-rs/core/src/tools/registry_tests.rs)

## Tradeoff

This is intentionally less invasive than openai#16627: it does **not** move
result boxing into every concrete handler and does **not** change
`ToolHandler` into an object-safe trait.

Instead, it keeps the existing registry-level type-erasure boundary and
only removes the macro-generated async wrapper layer from concrete
impls. So the runtime boxing story stays basically the same as before,
while the compile-time savings are still large.

## Verification

Existing verification for this branch still applies:

- Ran `cargo test -p codex-core`; this change compiled and the suite
reached the known unrelated `config::tests::*guardian*` failures, with
no local diff under `codex-rs/core/src/config/`.

Profiling commands used for the tables above:

- `cargo clean -p codex-core`
- `cargo +nightly build -p codex-core --lib -Z unstable-options
--timings=json`
- `cargo +nightly rustc -p codex-core --lib -- -Z time-passes -Z
time-passes-format=json`
- `cargo +nightly rustc -p codex-core --lib -- -Z self-profile=... -Z
self-profile-events=default,query-keys,args,llvm,artifact-sizes`
- `measureme summarize -p 0.5`

Author: bolinfest

codex-rs/core/src/tools/code_mode/execute_handler.rs

@@ -1,5 +1,3 @@
-use async_trait::async_trait;
-
 use crate::function_tool::FunctionCallError;
 use crate::tools::context::FunctionToolOutput;
 use crate::tools::context::ToolInvocation;
@@ -53,7 +51,6 @@ impl CodeModeExecuteHandler {
     }
 }
 
-#[async_trait]
 impl ToolHandler for CodeModeExecuteHandler {
     type Output = FunctionToolOutput;
 

codex-rs/core/src/tools/code_mode/wait_handler.rs

@@ -1,4 +1,3 @@
-use async_trait::async_trait;
 use serde::Deserialize;
 
 use crate::function_tool::FunctionCallError;
@@ -39,7 +38,6 @@ where
     })
 }
 
-#[async_trait]
 impl ToolHandler for CodeModeWaitHandler {
     type Output = FunctionToolOutput;
 

codex-rs/core/src/tools/handlers/agent_jobs.rs

@@ -13,7 +13,6 @@ use crate::tools::handlers::multi_agents::build_agent_spawn_config;
 use crate::tools::handlers::parse_arguments;
 use crate::tools::registry::ToolHandler;
 use crate::tools::registry::ToolKind;
-use async_trait::async_trait;
 use codex_protocol::ThreadId;
 use codex_protocol::protocol::AgentStatus;
 use codex_protocol::protocol::SessionSource;
@@ -178,7 +177,6 @@ impl JobProgressEmitter {
     }
 }
 
-#[async_trait]
 impl ToolHandler for BatchJobHandler {
     type Output = FunctionToolOutput;
 

codex-rs/core/src/tools/handlers/apply_patch.rs

@@ -21,7 +21,6 @@ use crate::tools::registry::ToolKind;
 use crate::tools::runtimes::apply_patch::ApplyPatchRequest;
 use crate::tools::runtimes::apply_patch::ApplyPatchRuntime;
 use crate::tools::sandboxing::ToolCtx;
-use async_trait::async_trait;
 use codex_apply_patch::ApplyPatchAction;
 use codex_apply_patch::ApplyPatchFileChange;
 use codex_protocol::models::FileSystemPermissions;
@@ -122,7 +121,6 @@ async fn effective_patch_permissions(
     )
 }
 
-#[async_trait]
 impl ToolHandler for ApplyPatchHandler {
     type Output = ApplyPatchToolOutput;
 

codex-rs/core/src/tools/handlers/dynamic.rs

@@ -7,7 +7,6 @@ use crate::tools::context::ToolPayload;
 use crate::tools::handlers::parse_arguments;
 use crate::tools::registry::ToolHandler;
 use crate::tools::registry::ToolKind;
-use async_trait::async_trait;
 use codex_protocol::dynamic_tools::DynamicToolCallRequest;
 use codex_protocol::dynamic_tools::DynamicToolResponse;
 use codex_protocol::models::FunctionCallOutputContentItem;
@@ -20,7 +19,6 @@ use tracing::warn;
 
 pub struct DynamicToolHandler;
 
-#[async_trait]
 impl ToolHandler for DynamicToolHandler {
     type Output = FunctionToolOutput;
 

codex-rs/core/src/tools/handlers/js_repl.rs

@@ -1,4 +1,3 @@
-use async_trait::async_trait;
 use serde_json::Value as JsonValue;
 use std::sync::Arc;
 use std::time::Duration;
@@ -92,7 +91,6 @@ async fn emit_js_repl_exec_end(
     };
     emitter.emit(ctx, stage).await;
 }
-#[async_trait]
 impl ToolHandler for JsReplHandler {
     type Output = FunctionToolOutput;
 
@@ -182,7 +180,6 @@ impl ToolHandler for JsReplHandler {
     }
 }
 
-#[async_trait]
 impl ToolHandler for JsReplResetHandler {
     type Output = FunctionToolOutput;
 

codex-rs/core/src/tools/handlers/list_dir.rs

@@ -4,7 +4,6 @@ use std::fs::FileType;
 use std::path::Path;
 use std::path::PathBuf;
 
-use async_trait::async_trait;
 use codex_utils_string::take_bytes_at_char_boundary;
 use serde::Deserialize;
 use tokio::fs;
@@ -45,7 +44,6 @@ struct ListDirArgs {
     depth: usize,
 }
 
-#[async_trait]
 impl ToolHandler for ListDirHandler {
     type Output = FunctionToolOutput;
 

codex-rs/core/src/tools/handlers/mcp.rs

@@ -1,4 +1,3 @@
-use async_trait::async_trait;
 use std::sync::Arc;
 
 use crate::function_tool::FunctionCallError;
@@ -10,7 +9,6 @@ use crate::tools::registry::ToolKind;
 use codex_protocol::mcp::CallToolResult;
 
 pub struct McpHandler;
-#[async_trait]
 impl ToolHandler for McpHandler {
     type Output = CallToolResult;
 

codex-rs/core/src/tools/handlers/mcp_resource.rs

@@ -3,7 +3,6 @@ use std::sync::Arc;
 use std::time::Duration;
 use std::time::Instant;
 
-use async_trait::async_trait;
 use codex_protocol::mcp::CallToolResult;
 use codex_protocol::models::function_call_output_content_items_to_text;
 use rmcp::model::ListResourceTemplatesResult;
@@ -178,7 +177,6 @@ struct ReadResourcePayload {
     result: ReadResourceResult,
 }
 
-#[async_trait]
 impl ToolHandler for McpResourceHandler {
     type Output = FunctionToolOutput;
 

codex-rs/core/src/tools/handlers/multi_agents.rs

@@ -17,7 +17,6 @@ pub(crate) use crate::tools::handlers::multi_agents_common::*;
 use crate::tools::handlers::parse_arguments;
 use crate::tools::registry::ToolHandler;
 use crate::tools::registry::ToolKind;
-use async_trait::async_trait;
 use codex_protocol::ThreadId;
 use codex_protocol::models::ResponseInputItem;
 use codex_protocol::openai_models::ReasoningEffort;