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fix(acp): per-runtime env defaults at spawn — isolate Hermes from configured MCP startup (#3420)

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## Summary

- add a generic per-runtime env-defaults table,
`config::default_agent_env()`, mirroring the existing
`default_agent_args()` / `codex_network_env()` precedent, and merge it
once in `AcpClient::spawn` with the established precedence: **runtime
defaults < persona `extra_env` < inherited parent env**
- first (and only) row: Buzz-owned Hermes processes get
`HERMES_ACP_SKIP_CONFIGURED_MCP=1`, so Hermes does not preload unrelated
profile-configured MCP servers before answering ACP `initialize` (fixes
the 10s model-discovery timeout in #3355 — Buzz supplies session MCP
servers explicitly through `session/new`, per Hermes's documented
host-integration contract for this variable)
- normalize Windows `.cmd`/`.bat` shims alongside `.exe` in
`normalize_agent_command_identity` (npm installs resolve to those
wrappers)
- switch the `extra_env` parent-presence check from `var()` to
`var_os()` so non-UTF-8 parent values are honored

Replaces the runtime-specific approach in #3386: same behavior, but the
mechanism is generic runtime spawn metadata in `config.rs` rather than a
Hermes/ACP special case in `acp.rs`, and the seam covers every launch
path (Desktop spawn, `buzz-acp models`, CLI) because they all funnel
through `AcpClient::spawn`. ~15 lines of production code.

Fixes #3355

## Testing

- `cargo test -p buzz-acp` — **639 passed, 0 failed** (full package,
includes the new `default_agent_env_recognizes_hermes_identities` unit
test and `spawn_applies_runtime_env_defaults_with_extra_env_precedence`
integration test covering default injection, extra_env override, and
non-Hermes exclusion)
- `cargo fmt --all -- --check`, `cargo clippy -p buzz-acp --all-targets
-- -D warnings` — clean
- live-local with real Hermes v0.19.0 (`hermes-acp`): `buzz-acp models`
returned **13 models / currentModelId in 2.6–3.0s** (was a 10.0s timeout
on the first cold run without isolation); a wrapper probe confirmed the
child received `HERMES_ACP_SKIP_CONFIGURED_MCP=1` by default and `0`
when the parent env set it explicitly (operator wins)
- lefthook pre-push suite green: rust-tests, desktop-check,
desktop-test, desktop-tauri-test, mobile-test, branch-skew

No UI changes; subprocess environment behavior only.

Signed-off-by: npub1qyvc0c5kl4gqv2fd97fsk46tu378sqgy35vc83rvgfwne90sel7s0ed67d <011987e296fd5006292d2f930b574be47c7801048d1983c46c425d3c95f0cffd@buzz.block.builderlab.xyz>
Signed-off-by: Tyler Longwell <tlongwell@block.xyz>
Co-authored-by: npub1qyvc0c5kl4gqv2fd97fsk46tu378sqgy35vc83rvgfwne90sel7s0ed67d <011987e296fd5006292d2f930b574be47c7801048d1983c46c425d3c95f0cffd@buzz.block.builderlab.xyz>
Co-authored-by: Tyler Longwell <tlongwell@block.xyz>
Co-authored-by: mr-r0b0t.eth <adam.manning@pro-serveinc.com>
This commit is contained in:
Tyler
2026-07-28 22:51:19 -04:00
committed by GitHub
co-authored by npub1qyvc0c5kl4gqv2fd97fsk46tu378sqgy35vc83rvgfwne90sel7s0ed67d Tyler Longwell mr-r0b0t.eth
parent 22be8bb351
commit 6300a6b1d0
2 changed files with 141 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
crates/buzz-acp/src/acp.rs
+83 -1
View File
@@ -494,12 +494,22 @@ impl AcpClient {
// entry falls through to the standard operator-wins treatment below.
let codex_merge_active = codex_config_value.is_some();
// Per-runtime environment defaults (e.g. Hermes MCP-startup isolation).
// Applied first so both persona `extra_env` (below, via `Command::env`
// key replacement) and inherited parent env (via the parent-presence
// check) override them.
for &(key, value) in crate::config::default_agent_env(command) {
if std::env::var_os(key).is_none() {
cmd.env(key, value);
}
}
for (key, value) in extra_env {
if key == "CODEX_CONFIG" && codex_merge_active {
// Handled by build_codex_config_env; skip here to avoid double-setting.
continue;
}
if std::env::var(key).is_err() {
if std::env::var_os(key).is_none() {
cmd.env(key, value);
}
}
@@ -2891,6 +2901,78 @@ mod tests {
);
}
/// Spawn a probe script whose file name carries a runtime identity (e.g.
/// `hermes-acp`) and return the value of `var` as the child observed it.
/// `<unset>` means the child did not receive the var.
#[cfg(unix)]
async fn spawn_named_and_read_child_env(
file_name: &str,
var: &str,
extra_env: &[(String, String)],
) -> String {
use std::os::unix::fs::PermissionsExt;
let dir = std::env::temp_dir().join(format!("buzz-acp-env-probe-{}", uuid::Uuid::new_v4()));
std::fs::create_dir_all(&dir).expect("create env probe dir");
let path = dir.join(file_name);
std::fs::write(
&path,
format!("#!/bin/sh\nprintf '%s\\n' \"${{{var}:-<unset>}}\"\n"),
)
.expect("write env probe script");
let mut permissions = std::fs::metadata(&path).expect("stat probe").permissions();
permissions.set_mode(0o700);
std::fs::set_permissions(&path, permissions).expect("chmod probe");
let mut client = AcpClient::spawn(
path.to_str().expect("probe path is UTF-8"),
&[],
extra_env,
false,
)
.await
.expect("spawn env probe script");
let observed = client
.reader
.next()
.await
.unwrap_or_else(|| panic!("child produced no output for {var}"))
.expect("child stdout was not readable");
client.shutdown().await;
std::fs::remove_dir_all(&dir).expect("remove env probe dir");
observed
}
/// Buzz-owned Hermes processes get the configured-MCP isolation default,
/// and an explicit persona entry still overrides it (defaults are applied
/// before `extra_env`, so the later `Command::env` write wins).
#[cfg(unix)]
#[tokio::test]
async fn spawn_applies_runtime_env_defaults_with_extra_env_precedence() {
const VAR: &str = "HERMES_ACP_SKIP_CONFIGURED_MCP";
if std::env::var_os(VAR).is_some() {
// Inherited parent values win over both layers; the default and
// override behavior below is unobservable in such an environment.
return;
}
assert_eq!(
spawn_named_and_read_child_env("hermes-acp", VAR, &[]).await,
"1",
"Hermes spawns must default {VAR}=1"
);
assert_eq!(
spawn_named_and_read_child_env("hermes-acp", VAR, &[(VAR.into(), "0".into())]).await,
"0",
"an explicit extra_env entry must override the runtime default"
);
assert_eq!(
spawn_named_and_read_child_env("other-agent", VAR, &[]).await,
"<unset>",
"non-Hermes spawns must not receive Hermes defaults"
);
}
/// Persona config must not be able to re-enable the scheduler: this is a
/// correctness invariant, not an operator-tunable default, so the
/// injection is set after (and therefore wins over) the `extra_env` loop.
crates/buzz-acp/src/config.rs
+58 -1
View File
@@ -676,7 +676,12 @@ pub(crate) fn normalize_agent_command_identity(command: &str) -> String {
.next()
.expect("rsplit always yields at least one element");
let lower = basename.to_ascii_lowercase();
let stem = lower.strip_suffix(".exe").unwrap_or(&lower);
// Windows resolves commands through `.exe` binaries and npm's `.cmd`/`.bat`
// shims; all three name the same runtime identity.
let stem = [".exe", ".cmd", ".bat"]
.iter()
.find_map(|extension| lower.strip_suffix(extension))
.unwrap_or(&lower);
stem.chars()
.map(|character| match character {
' ' | '_' => '-',
@@ -694,6 +699,25 @@ fn default_agent_args(command: &str) -> Option<Vec<String>> {
}
}
/// Per-runtime environment defaults applied when Buzz owns the agent process.
///
/// Mirrors [`default_agent_args`]: keyed on the normalized command identity,
/// with the merge (in `AcpClient::spawn`) giving explicit persona env and
/// inherited parent env precedence over these defaults.
///
/// Hermes: ACP hosts supply session MCP servers explicitly through
/// `session/new`, but Hermes otherwise starts every profile-configured MCP
/// server before it responds to `initialize` — which can exhaust the host's
/// startup budget (see block/buzz#3355). Skip that unrelated global startup
/// by default; an operator or persona can still opt back in by setting the
/// variable explicitly.
pub(crate) fn default_agent_env(command: &str) -> &'static [(&'static str, &'static str)] {
match normalize_agent_command_identity(command).as_str() {
"hermes" | "hermes-agent" | "hermes-acp" => &[("HERMES_ACP_SKIP_CONFIGURED_MCP", "1")],
_ => &[],
}
}
/// Build the `CODEX_CONFIG` environment variable that enables full outbound
/// network access in Codex's macOS Seatbelt sandbox.
///
@@ -1589,6 +1613,15 @@ mod tests {
"claude-code"
);
assert_eq!(normalize_agent_command_identity("Goose.EXE"), "goose");
// Windows npm shims resolve to `.cmd`/`.bat` wrappers.
assert_eq!(
normalize_agent_command_identity(r"C:\Users\test\AppData\Roaming\npm\hermes-acp.cmd"),
"hermes-acp"
);
assert_eq!(
normalize_agent_command_identity(r"C:\Tools\Hermes\HERMES-AGENT.BAT"),
"hermes-agent"
);
// Non-ASCII must not panic.
assert_eq!(normalize_agent_command_identity("my-agënt"), "my-agënt");
// Edge cases: empty, whitespace-only, bare separators.
@@ -1598,6 +1631,30 @@ mod tests {
assert_eq!(normalize_agent_command_identity("///"), "");
}
#[test]
fn default_agent_env_recognizes_hermes_identities() {
for command in [
"hermes",
"hermes-agent",
"hermes-acp",
"/opt/hermes/bin/hermes-acp",
r"C:\Users\test\bin\HERMES_ACP.EXE",
r"C:\Users\test\AppData\Roaming\npm\hermes-acp.cmd",
] {
assert_eq!(
default_agent_env(command),
&[("HERMES_ACP_SKIP_CONFIGURED_MCP", "1")],
"unexpected env defaults for {command}"
);
}
for command in ["goose", "codex-acp", "claude-agent-acp", "buzz-agent", ""] {
assert!(
default_agent_env(command).is_empty(),
"non-Hermes command must have no env defaults: {command}"
);
}
}
#[test]
fn strips_legacy_acp_arg_case_insensitively() {
assert_eq!(