audit: consolidate duplicated board / config resolution call sites across the workspace #519

Background

While fixing #515 / #518 it became clear that fbuild has several near-duplicate code paths that all want to resolve a board id (and other config pieces) but each reach for the underlying primitive independently. Every time one of those primitives gains a new parameter — like the recently added project_dir for project-local boards/*.json — every call site has to be updated by hand, and missing one is silent (the build just behaves as if the new feature isn't there).

The proximate example: #516 added BoardConfig::from_board_id_in_project(..., project_dir) and updated compile_many::platform_for_board. But pipeline::BuildContext::new_with_perf (the daemon's actual fbuild build path) and script_runtime::build_script_runtime_board_config were both missed — they kept calling the legacy from_board_id and silently dropped the project_dir context. End users still saw unknown board 'X' (no built-in defaults) even though the underlying lookup primitive could find it. PR #518 catches them up, but the structural issue remains.

Ask

Audit the workspace for duplicated config-resolution logic and consolidate into a small set of shared entry points that take ALL needed context (project_dir, env_name, overrides, etc.) once. Concretely:

Board lookup (immediate)

• crates/fbuild-build/src/compile_many.rs:platform_for_board
• crates/fbuild-build/src/pipeline/context.rs:BuildContext::new_with_perf
• crates/fbuild-build/src/script_runtime.rs:build_script_runtime_board_config
• crates/fbuild-cli/src/cli/deploy.rs:run_deploy (two consecutive from_board_id calls with a fallback pattern repeated 3+ times in daemon/src/handlers/operations/deploy.rs)
• crates/fbuild-daemon/src/handlers/operations/deploy.rs — there are ~5 instances of the same from_board_id(&board_id, &deploy_board_overrides).or_else(|_| from_board_id(&board_id, &HashMap::new())) pattern (lines ~154, ~427, ~667, ~699). That fallback strongly suggests a shared helper.

Other likely candidates worth checking

• platformio.ini reading: are there multiple places that parse / hold a PlatformIOConfig per build? from_path + from_path_with_overrides + get_env_config are called from many sites.
• project_dir handling: many places independently derive things like project_dir.join(\"platformio.ini\"), project_dir.join(\".fbuild\"), etc.
• toolchain resolution + extra-script overlay setup — large per-orchestrator copies might share a common pre-build shim.

Proposed shape

A small fbuild_build::resolution (or similar) module with a couple of entry points:

pub struct ResolutionContext<'a> {
    pub project_dir: &'a Path,
    pub env_name:    &'a str,
    pub config:      &'a PlatformIOConfig,
    pub board_overrides: &'a HashMap<String, String>,
}

impl ResolutionContext<'_> {
    pub fn resolve_board(&self) -> Result<BoardConfig> { ... }
    pub fn resolve_platform(&self) -> Result<Platform> { ... }
    pub fn resolve_extra_script_overlay(&self) -> Result<BuildOverlay> { ... }
}

Then every existing site becomes one call instead of three. Adding the next parameter is then a one-line change to the context struct rather than a workspace-wide rename.

Acceptance

• A single grep for BoardConfig::from_board_id (and variants) returns ≤2 call sites outside fbuild-config (the new entry points + one test helper), down from the ~12 production sites today.
• Tests still green, no behavior change.
• A short doc comment on the new module pointing future feature work at the right injection point.

Why now

Every feature that adds a knob (project_dir was just the most recent) gets paid for N times instead of once, and N-1 of those payments are silent regressions waiting for a CI run to surface them. This is cheap to consolidate while the call-site list is still small enough to enumerate.

Filed alongside #518 (which is the minimum fix to unblock the immediate user).