feat: add config structs for services with inline env var config

[geoffjay]

Creates dedicated config.rs modules for the six services that previously had all configuration read inline in main.rs: core, orchestrator, wrap, ask, notify, and communicate.

Each config struct follows the same pattern as the services migrated in #1204:

1. Load base values from agentd_common::config::load()
2. Overlay legacy AGENTD_* environment variables for backward compatibility
3. Replace all inline env::var() calls in main.rs with config struct field access

The wrap and orchestrator backends continue to use BackendType::from_env_strict() for backend selection — that function already encapsulates AGENTD_BACKEND parsing with proper error messages.

Closes #1197

[geoffjay]

Review: feat: add config structs for services with inline env var config

Stack Position

This PR sits at the top of a blocked stack:

This PR cannot merge until the chain below it is resolved. The blocking issues in #1201 (AGENTD_HISTORY_SIZE collision, incomplete env var table, orchestrator rename) and the missing-test issue in #1203 propagate upward.

---

Blocking Issues

1. Silent config-file errors via unwrap_or_default() — all six new config.rs files

Same issue flagged in #1204. Every service's load() calls:

let shared = agentd_common::config::load().unwrap_or_default();

If the TOML config file is present but malformed, this silently returns Default::default() — the operator gets no error message, no log line, and no indication that their config was ignored. This will be extremely painful to debug in production.

Required fix in all six files (ask, communicate, core, notify, orchestrator, wrap):

let shared = agentd_common::config::load().unwrap_or_else(|e| {
    tracing::warn!(
        "failed to load config file, using compiled defaults: {e:#}"
    );
    agentd_common::config::AgentdConfig::default()
});

2. Diagnostic regression in crates/wrap/src/main.rs

The old main.rs had three explicit warn!() calls for invalid env var values:

warn!("AGENTD_WRAP_HISTORY_BYTES={:?} is not a valid usize; using default {} bytes", raw, DEFAULT_HISTORY_BYTES);
warn!("AGENTD_WRAP_CHANNEL_CAPACITY={:?} is not a valid usize; using default {}", raw, DEFAULT_CHANNEL_CAPACITY);
warn!("AGENTD_WRAP_CHANNEL_CAPACITY=0 is invalid; clamped to 1");

These were deleted in this PR but not moved into WrapConfig::load(). The new load() silently clamps or defaults bad values without telling the operator. The test test_channel_capacity_zero_clamped_to_one is a good sign — but a test passing silently doesn't help an operator who set AGENTD_WRAP_CHANNEL_CAPACITY=abc and wonders why their config was ignored.

Required fix — add warn! in WrapConfig::load() for each fallback:

// history_bytes
let history_bytes = std::env::var("AGENTD_WRAP_HISTORY_BYTES")
    .ok()
    .and_then(|v| {
        v.parse::<usize>().map_err(|_| {
            tracing::warn!(
                "AGENTD_WRAP_HISTORY_BYTES={v:?} is not a valid usize; using default {} bytes",
                DEFAULT_HISTORY_BYTES
            );
        }).ok()
    })
    .unwrap_or(base.history_bytes);

// channel_capacity (with clamp-to-1 warn)
let channel_capacity = std::env::var("AGENTD_WRAP_CHANNEL_CAPACITY")
    .ok()
    .and_then(|v| {
        v.parse::<usize>().map_err(|_| {
            tracing::warn!(
                "AGENTD_WRAP_CHANNEL_CAPACITY={v:?} is not a valid usize; using default {}",
                DEFAULT_CHANNEL_CAPACITY
            );
        }).ok()
    })
    .unwrap_or(base.channel_capacity);
let channel_capacity = if channel_capacity == 0 {
    tracing::warn!("AGENTD_WRAP_CHANNEL_CAPACITY=0 is invalid; clamped to 1");
    1
} else {
    channel_capacity
};

---

Non-Blocking Suggestions

crates/wrap/src/config.rs — TODO comments on hardcoded defaults

WrapConfig::load() falls back to DEFAULT_HISTORY_BYTES and DEFAULT_CHANNEL_CAPACITY constants rather than the shared schema fields (base.history_bytes, base.channel_capacity). This is expected given the schema gaps noted in #1201 (WrapConfig in shared schema is missing these fields). Leave a // TODO: use base.history_bytes once WrapConfig schema is complete comment so the gap is trackable.

crates/orchestrator/src/config.rs — unused port variable

There is a let port = ... binding that appears to be unused — it's computed but not stored in the returned OrchestratorConfig. Either include it in the struct or remove it to silence the dead-code warning.

---

What's Working Well

• All test modules correctly acquire ENV_LOCK before mutating env vars
• Save/restore/remove pattern is applied consistently: env vars are removed before the assert so a panic during setup doesn't leak state into other tests
• The test_channel_capacity_zero_clamped_to_one test in wrap is a nice edge-case addition
• Service-local config.rs modules are a clean separation from main.rs config wiring

---

Summary

Two blocking issues must be fixed before merge:

1. All six load() functions need unwrap_or_else with a tracing::warn! instead of silent unwrap_or_default()
2. WrapConfig::load() must restore the diagnostic warn!() calls that were removed from wrap/main.rs

This PR also needs a restack once #1201–#1204 are resolved.

[geoffjay]

This change is part of the following stack:

• feat(common): add config module with TOML schema and layered loading #1201
  • test(common): add integration tests for layered config precedence #1202
    • feat(cli): add config init and config show subcommands #1203
      • refactor: migrate services with existing config.rs to shared TOML config #1204
        • feat: add config structs for services with inline env var config #1205 ◀
          • feat(config): add ValidateConfig trait and per-service validation #1224
            • docs: add configuration system documentation #1207

_{Change managed by git-spice.}