build: replace argument dispatch and retain source-bound verification

Replace argument recovery with direct build targets. Run host, target,
board, coverage, Miri and selected Kani checks while retaining source
identities, logs and artifacts, including failed attempts.

Keep the PID proof diagnostic exception explicit and match its exact
identity alongside passing contract assertions and covers.

Validation: final-source verification matrix, assembled workflow tests
and documentation build.

firmware/boards/Makefile

@@ -1,44 +1,31 @@
-override SHELL := /bin/sh
-override MAKEFLAGS += --no-print-directory
+SHELL := /bin/sh
+MAKEFLAGS += --no-print-directory
+export CARGO_BUILD_JOBS ?= 2
 
 .DEFAULT_GOAL := help
 .DELETE_ON_ERROR:
 
-override CARGO := cargo
-override CARGO_FLAGS := --locked --offline
-
 override EMBEDDED_TARGET := thumbv7em-none-eabihf
-override TARGET_DIR := ../target/$(EMBEDDED_TARGET)/release
-override SCRIPTS_DIR := ../scripts
+CARGO_TARGET_DIR ?= ../target
+override TARGET_DIR := $(CARGO_TARGET_DIR)/$(EMBEDDED_TARGET)/release
 
 override BOARDS := geprc-f722-v2 kakute-f7-mini-v3
 override BOARD_PACKAGES := $(addprefix kaptan-,$(BOARDS))
 override BOARD_PACKAGE_ARGS := $(addprefix -p ,$(BOARD_PACKAGES))
+override BOARD_BIN_ARGS := $(addprefix --bin ,$(BOARD_PACKAGES))
 
-override PRIMARY_GOAL := $(firstword $(MAKECMDGOALS))
-
-run:
-	@exec python3 ../../scripts/make-argv.py exec run $(CARGO) build --release \
-		$(CARGO_FLAGS) $(BOARD_PACKAGE_ARGS) --target $(EMBEDDED_TARGET)
-	@set -e; for board in $(BOARD_PACKAGES); do \
-		$(SCRIPTS_DIR)/create-dfu-image.sh $(TARGET_DIR)/$$board; \
-	done
-
-ifeq ($(PRIMARY_GOAL),run)
-
-.PHONY: run
-
-# Application arguments may also look like Make goals. The run recipe recovers
-# their exact boundaries from the original invocation.
-.DEFAULT:
-	@:
-
-else
-
-.PHONY: help run
+.NOTPARALLEL:
+.PHONY: help build
 
 help:
-	@printf '%s\n' 'Usage: make firmware/boards -- <cargo build arguments...>' '' \
-		'With no arguments, every board is built and packaged.'
+	@printf '%s\n' 'Usage: make -C firmware/boards build' '' \
+		'  build  Build and package every board in release mode' \
+		'CARGO_TARGET_DIR defaults to firmware/target; relative overrides are relative to firmware/boards/.' \
+		'For one board: make -C firmware/boards/<board> build|flash'
 
-endif
+build:
+	cargo build --release --locked --offline $(BOARD_PACKAGE_ARGS) $(BOARD_BIN_ARGS) \
+		--target $(EMBEDDED_TARGET) --target-dir "$(CARGO_TARGET_DIR)"
+	@set -e; for board in $(BOARD_PACKAGES); do \
+		../scripts/create-dfu-image.sh "$(TARGET_DIR)/$$board"; \
+	done