WASM Engine ABI

The browser build of kapi (kapi/cmd/kapi-wasm-cli) registers a set of global JS functions at boot. That set is a versioned contract, the ABI consumed by the @neokapi/engine npm package (packages/engine), which wraps it in the typed KapiRuntime facade.

Contract

• Single registration point. Every entry point is declared in the engineExports table in kapi/cmd/kapi-wasm-cli/main.go and installed on globalThis from there. Nothing else registers engine globals.
• Feature detection. kapiEngineABI() returns {abi, version, functions}: the ABI major version, the kapi build version, and the list of registered global names. A build without kapiEngineABI predates the descriptor and is treated as abi 0 (probe individual globals).
• Additive within a version. For one abi value, changes are strictly additive: new functions may appear in functions, but existing names, signatures, and payload shapes never change or disappear. Renaming or removing an entry point, or changing a signature incompatibly, bumps the version.
• Boot handshake. The host installs its fs/process shims (the wasm_exec.js environment) before instantiation; after registering the globals, the engine invokes the host's __kapiCliReady() callback and then blocks forever so the globals stay callable.
• Reverse bridges. Some features call back into optional host-provided globals: __kapiPdfium (PDF text + geometry), kapiLocalGenerate (on-device LLM), kapiLocalNER (on-device NER), and kapiBrowserTranslate (with the platform Translator API). Each degrades with an actionable error when its bridge is absent. The typed interfaces live in packages/engine/src/capabilities.ts.

Command surface

kapiRun(argv) executes the ordinary kapi CLI, so the browser build has a second contract alongside the global function set: which verbs it answers.

• One declaration. cli.BrowserCommandSet is the browser build's command set, mirroring cli.KapiCommandSet (the native binary's) verb for verb. kapi/cmd/kapi-wasm-cli registers it wholesale and declares nothing itself.
• No missing verbs. A verb the browser cannot run (one needing a subprocess, the OS keychain, the network, or a socket) is recorded in cli.browserGaps with the facility it needs, and registers a command that reports it. unknown command therefore means the verb does not exist in kapi at all, never that the browser omitted it. --help still works on those verbs; their help text carries the limitation.
• Drift is a test failure. cli.TestBrowserCommandSurface compares the two sets and fails when a verb appears in one and not the other, or when a gap's help metadata drifts from the command it stands in for. Adding a verb to KapiCommandSet is a decision: wire it up for the browser, or record why it cannot run there.
• Runtime guard. make wasm-surface-smoke (scripts/verify-snippets/command-surface-smoke.ts) boots the real wasm in Node, sweeps every reachable verb for unknown command, asserts each gap's message, and replays the argv the lab explorers themselves use. It runs in the docs snippet-verification workflow (docs-verify-snippets.yml).
• Capture strips ANSI. The engine boots with CLICOLOR_FORCE=1 so the playground terminal renders kapi's real styling; runCapture hands output to program code instead, and strips the escapes so a --json payload parses.

The same derivation feeds the docs: scripts/gen-refs reads cli.BrowserUnavailableReason for each command's runnable-in-browser badge, so the Command Reference cannot claim a verb runs in the lab when it does not.

Where the pieces live

Concern	Location
Registration table + kapiEngineABI()	kapi/cmd/kapi-wasm-cli/main.go
Browser command set + recorded gaps	cli/browsercmds.go
Surface drift guard	cli/browsercmds_test.go
Runtime surface smoke	scripts/verify-snippets/command-surface-smoke.ts
Ambient TS typings for the globals	packages/engine/src/globals.ts
Wire shapes + engineABI() helper	packages/engine/src/abi.ts
KapiRuntime facade + boot	packages/engine/src/runtime.ts
Reverse-bridge capability types	packages/engine/src/capabilities.ts
Payload types (ContentTree, runs)	@neokapi/contract-types (generated)

When adding an entry point: add it to engineExports, type it in globals.ts, surface it on the facade if user-facing, and leave the abi value alone (additions don't bump it).