Environment variables

This page lists the supported runtime variables and the main developer overrides. Most runtime numbers and booleans are parsed by rom_weaver_core::env; the table notes exceptions.

Command-scoped configuration

Patch metadata and browser command arguments are command inputs, not ambient environment configuration. SOLID metadata is supplied with the patch create --solid-* flags documented in patch creation metadata, or with the corresponding solid_* fields on a typed WASM PatchCreateCommand.

The browser OPFS runner likewise has no constructor-level program, argv0, or env options. WASI argv0 is always rom-weaver. A command may still supply env in its per-run options when it needs one of the runtime knobs below.

Runtime knobs

Variable	Type	Default	Read at	Purpose
`ROM_WEAVER_LOG`	filter string	unset	`crates/rom-weaver-cli/src/lib.rs`	Tracing filter spec (e.g. `rom_weaver_app=trace`); also honored via `RUST_LOG` when no explicit CLI log level is selected.
`ROM_WEAVER_PATCH_IN_MEMORY_LIMIT`	u64 (bytes)	256 MiB	`crates/rom-weaver-patches/src/lib.rs`	Cap below which patch apply/create buffers in memory; above it the streaming path is used. Set to `0` to force streaming for benchmarks.
`ROM_WEAVER_DISC_TRACK_IN_MEMORY_LIMIT`	u64 (bytes)	256 MiB	`crates/rom-weaver-cli/src/patch_apply_disc.rs`	Cap for buffering a single freshly produced disc track in memory during compression instead of a temp file (only ever bounds one track, never the whole disc). Set to `0` to force the on-disk path for regression/parity runs.
`ROM_WEAVER_ZIP_ZSTD_MEM_BUDGET_MB`	u64 (MiB)	physical RAM / 2 (1-2 GiB fallback)	`crates/rom-weaver-containers/src/handlers/zip.rs`	Memory budget that caps zstd multi-thread job count for zip create.
`ROM_WEAVER_7Z_MEM_BUDGET_MB`	u64 (MiB)	physical RAM / 2 (1 GiB wasm / 2 GiB native fallback)	`crates/rom-weaver-containers/src/handlers/sevenz.rs`	Memory budget that caps the LZMA2 multi-thread count for 7z create. Invalid text is ignored.
`ROM_WEAVER_7Z_ENCODER`	`liblzma`	7-Zip SDK encoder	`handlers/sevenz.rs` planner and `archive_write_set_format_7zip.c` writer (raw `getenv`)	Selects the seeded parallel-block liblzma LZMA2 encoder for 7z create instead of the default 7-Zip SDK one. Output is slightly smaller than 7zz's, at a large time cost on inputs bigger than the dictionary; any other value keeps the SDK encoder. Native builds only - the wasm build never compiles the SDK encoder in, so it always uses liblzma and ignores this.

Test / build-only knobs

Not for production use.

Variable	Read at	Purpose
`ROM_WEAVER_TEST_THREAD_POOL_FAIL`	`crates/rom-weaver-core/src/threads.rs`	Forces a thread-pool build failure to exercise the single-thread fallback.
`ROM_WEAVER_TEST_TMPDIR`	container test harness	Overrides the temp dir used by container tests.
`ROM_WEAVER_WASI_THREADS`	crate `build.rs` scripts	Forces the `rom_weaver_wasi_threads` cfg on (otherwise gated on the `wasm32-wasip1-threads` target).
`ROM_WEAVER_LZMA_ASM`	`crates/rom-weaver-containers/libarchive/build.rs`	Names the MASM-compatible assembler used for the x86-64 LZMA decode loop, replacing the `jwasm`/`asmc`/`asmc64`/`uasm`/`ml64` probe. Missing or failing assemblers fall back to the portable C loop with a build warning, never an error. Read only on x86-64 targets.
`ROM_WEAVER_UASM`	`crates/rom-weaver-containers/libarchive/build.rs`	Alias for `ROM_WEAVER_LZMA_ASM`. Both are honoured; when both are set `ROM_WEAVER_LZMA_ASM` is tried first and `ROM_WEAVER_UASM` is the fallback candidate.

Browser / PWA runtime handles (`window.*` globals)

Not env vars: these are diagnostic and service-worker handles exposed by the webapp at runtime, not process environment variables.

Global	Direction	Set/read at	Purpose
`window.ROM_WEAVER_CONSOLE_LOGS`	exposed by app	`webapp/console-log-capture.ts`	Console-log capture API (`getReport`/`copy`/`clear`/...) for debugging.
`window.ROM_WEAVER_SERVICE_WORKER`	exposed by app	`webapp/webapp.ts`	Service-worker cache controls (`forceCacheAndReload`/`getState`/...).
`window.ROM_WEAVER_BROWSER_DIAGNOSTICS`	exposed by app	`webapp/browser-runtime-diagnostics.ts`	Browser runtime diagnostics handle.
`window.ROM_WEAVER_MOBILE_SAFARI_DIAGNOSTICS`	exposed by app	`webapp/browser-runtime-diagnostics.ts`	Mobile-Safari runtime diagnostics handle (alias of the same diagnostics API).
`window.ROM_WEAVER_IOS_SAFARI_MATRIX`	exposed by app	`webapp/mobile-safari-matrix.ts`	iOS-Safari format-matrix diagnostic harness API (diagnostic page only).

Webapp build/test/bench tooling (`*.mjs`)

The webapp build/test/bench also reads a ROM_WEAVER_* family in *.mjs (vite/vitest configs, scripts) - e.g. ROM_WEAVER_APP_VERSION, ROM_WEAVER_COMMIT_HASH, ROM_WEAVER_WASM_ARTIFACT_DIR, ROM_WEAVER_COVERAGE, ROM_WEAVER_BROWSER, ROM_WEAVER_WASM_STRESS_1GB, and the ROM_WEAVER_WASM_BENCH* benchmark toggles. Those are front-end tooling knobs, not part of the Rust runtime surface above.