refactor(mobile): drop the range capability read and its session threading

The phone will read rangeBytes off the loose manifest reply instead, so
the read-method module goes and the session effects and hook return to
the pipeline branch's version. Range imports move to the bundle RPC
contract, the reply reader reuses the shared SHA256_PATTERN, and a new
test pins that node's level-6 gzip from the host encoder inflates with
fflate to the same bytes. The fetch and window-read modules still import
the deleted names until part 2.

Claude-Session: https://claude.ai/code/session_01JNnE9qzUZMMnqpZWCqM3nb

mobile/src/mobile-web-shell/mobile-web-shell-session-effects.test.ts

@@ -4,7 +4,7 @@ import type { MobileWebShellSessionEvent } from './mobile-web-shell-session-cont
 /** Each place a read of the host's generation can fail, and the cause it reports. */
 const doubles = vi.hoisted(() => ({
   manifest: (): Promise<unknown> => Promise.reject(new Error('no manifest staged')),
-  fetch: (_args: unknown): Promise<unknown> => Promise.reject(new Error('no fetch staged'))
+  fetch: (): Promise<unknown> => Promise.reject(new Error('no fetch staged'))
 }))
 
 vi.mock('expo-file-system', () => ({ Directory: class {}, File: class {}, Paths: { cache: '' } }))
@@ -13,13 +13,9 @@ vi.mock('../transport/rpc-operation', () => ({
   runRpcOperation: () => doubles.manifest()
 }))
 vi.mock('../transport/mobile-web-bundle-fetch', () => ({
-  fetchMobileWebBundle: (args: unknown) => doubles.fetch(args)
+  fetchMobileWebBundle: () => doubles.fetch()
 }))
 
-import {
-  MOBILE_WEB_BUNDLE_CAPABILITY,
-  MOBILE_WEB_BUNDLE_RANGE_CAPABILITY
-} from '../../../src/shared/mobile-web-bundle/mobile-web-bundle-capability'
 import { MobileWebBundleFetchError } from '../transport/mobile-web-bundle-fetch-refusal'
 import { markRpcDeliveryUnknown } from '../transport/rpc-delivery-ambiguity'
 import type { RpcClient } from '../transport/rpc-client'
@@ -81,15 +77,10 @@ function collect(): {
   return { events, send: (event) => events.push(event) }
 }
 
-async function runDownload(
-  client: RpcClient | null,
-  store: GenerationStore,
-  hostCapabilities: readonly string[] = [MOBILE_WEB_BUNDLE_CAPABILITY]
-) {
+async function runDownload(client: RpcClient | null, store: GenerationStore) {
   const { events, send } = collect()
   await download({
     client,
-    hostCapabilities,
     store,
     hostKey: 'k',
     flow: 3,
@@ -177,19 +168,4 @@ describe('the download', () => {
   it('that lands whole reports no failure', async () => {
     expect(await runDownload(CLIENT, storeThat(null))).toEqual([])
   })
-
-  it('pages a host that advertised ranges in ranges, and any other in chunks', async () => {
-    const seen: unknown[] = []
-    const landed = doubles.fetch
-    doubles.fetch = (args) => {
-      seen.push(args)
-      return landed(args)
-    }
-    await runDownload(CLIENT, storeThat(null), [
-      MOBILE_WEB_BUNDLE_CAPABILITY,
-      MOBILE_WEB_BUNDLE_RANGE_CAPABILITY
-    ])
-    await runDownload(CLIENT, storeThat(null))
-    expect(seen).toMatchObject([{ readMethod: 'range' }, { readMethod: 'chunk' }])
-  })
 })

mobile/src/mobile-web-shell/mobile-web-shell-session-effects.ts

@@ -1,6 +1,5 @@
 import { fetchMobileWebBundle } from '../transport/mobile-web-bundle-fetch'
 import { mobileWebBundleManifestRead } from '../transport/mobile-web-bundle-operations'
-import { mobileWebBundleReadMethodFor } from '../transport/mobile-web-bundle-read-method'
 import { runRpcOperation } from '../transport/rpc-operation'
 import type { RpcClient } from '../transport/rpc-client'
 import type { GenerationStore } from './generation-store'
@@ -92,8 +91,6 @@ export async function readManifest(
 
 export async function download(args: {
   client: RpcClient | null
-  /** The capabilities the gates proved for this connection, which name the read method. */
-  hostCapabilities: readonly string[]
   store: GenerationStore
   hostKey: string
   flow: number
@@ -114,7 +111,6 @@ export async function download(args: {
   try {
     const fetched = await fetchMobileWebBundle({
       client,
-      readMethod: mobileWebBundleReadMethodFor(args.hostCapabilities),
       signal: controller.signal,
       onProgress: (progress) => send({ type: 'fetch-progress', flow, ...progress })
     })

mobile/src/mobile-web-shell/use-mobile-web-shell-session.ts

@@ -168,8 +168,6 @@ export function useMobileWebShellSession(args: {
         case 'download':
           await download({
             client,
-            // The gates the reducer decided to download under, not a later render's.
-            hostCapabilities: sessionRef.current.gates?.hostCapabilities ?? [],
             store,
             hostKey,
             flow,

mobile/src/transport/mobile-web-bundle-operations.ts

@@ -2,9 +2,9 @@ import {
   MobileWebBundleErrorCodeSchema,
   MOBILE_WEB_BUNDLE_CHUNK_METHOD,
   MOBILE_WEB_BUNDLE_MANIFEST_METHOD,
+  MOBILE_WEB_BUNDLE_RANGE_METHOD,
   type MobileWebBundleErrorCode
 } from '../../../src/shared/mobile-web-bundle/bundle-rpc-contract'
-import { MOBILE_WEB_BUNDLE_RANGE_METHOD } from '../../../src/shared/mobile-web-bundle/bundle-range-rpc-contract'
 import {
   MobileWebBundleChunkReplySchema,
   MobileWebBundleManifestReplySchema,
@@ -39,8 +39,8 @@ export const mobileWebBundleChunkRead = defineRpcOperation({
   read: rpcResultVariant('mobile-web-bundle-chunk', MobileWebBundleChunkReplySchema)
 })
 
-/** Up to 384 KiB of one asset, gzipped when that shrinks it. Only sent to a host that advertised
- *  `mobileWeb.bundle.range.v1`; see `mobile-web-bundle-read-method.ts`. */
+/** One 384 KiB window of an asset, gzipped when that shrinks it. Only sent to a host whose manifest
+ *  reply named `rangeBytes`. */
 export const mobileWebBundleRangeRead = defineRpcOperation({
   name: 'mobileWeb.bundle-range',
   method: MOBILE_WEB_BUNDLE_RANGE_METHOD,

mobile/src/transport/mobile-web-bundle-range-decode.ts

@@ -5,7 +5,8 @@ import { MobileWebBundleFetchError } from './mobile-web-bundle-fetch-refusal'
  * The raw bytes of one range, from the `dataBase64` bytes the host sent under `encoding`.
  *
  * Inflated into a buffer one byte past the window: fflate fills a supplied `out` and never grows it,
- * so a gzip bomb costs at most that allocation, and a body that fills the spare byte is overlong.
+ * so a gzip bomb costs at most that much memory (not time: inflating still runs to the body's end),
+ * and a body that fills the spare byte is overlong.
  */
 export function decodeMobileWebBundleRange(
   range: { readonly path: string; readonly offset: number; readonly encoding: string },

mobile/src/transport/mobile-web-bundle-range-interop.test.ts

@@ -0,0 +1,38 @@
+import { randomBytes } from 'node:crypto'
+import { gunzipSync } from 'fflate'
+import { describe, expect, it } from 'vitest'
+import { encodeMobileWebBundleRange } from '../../../src/main/runtime/rpc/methods/mobile-web-bundle-range-encoding'
+import { MOBILE_WEB_BUNDLE_RANGE_BYTES } from '../../../src/shared/mobile-web-bundle/bundle-rpc-contract'
+
+/** Script-like and a full range long, so the host's level-6 deflate emits dynamic Huffman blocks. */
+function scriptRange(): Buffer {
+  const words = ['const ', 'function ', 'return ', 'export ', '=> ', '{', '}', ';\n', 'orca']
+  let text = ''
+  for (let index = 0; text.length < MOBILE_WEB_BUNDLE_RANGE_BYTES; index += 1) {
+    text += words[(index * 7) % words.length] + String(index % 1000)
+  }
+  return Buffer.from(text.slice(0, MOBILE_WEB_BUNDLE_RANGE_BYTES))
+}
+
+// The host deflates with node's zlib and the phone inflates with fflate: two implementations that
+// must agree on every range the host can send.
+describe('a host-encoded range decoded by the phone', () => {
+  it('inflates node gzip output with fflate to the same bytes', async () => {
+    const raw = scriptRange()
+    const encoded = await encodeMobileWebBundleRange(raw)
+
+    expect(encoded.encoding).toBe('gzip')
+    const inflated = gunzipSync(new Uint8Array(encoded.bytes), {
+      out: new Uint8Array(raw.byteLength + 1)
+    })
+    expect(Buffer.from(inflated).equals(raw)).toBe(true)
+  })
+
+  it('leaves incompressible bytes as identity, which needs no decoder', async () => {
+    const raw = randomBytes(4096)
+    const encoded = await encodeMobileWebBundleRange(raw)
+
+    expect(encoded.encoding).toBe('identity')
+    expect(encoded.bytes.equals(raw)).toBe(true)
+  })
+})

mobile/src/transport/mobile-web-bundle-range-reply.test.ts

@@ -2,14 +2,9 @@ import { describe, expect, it } from 'vitest'
 import {
   MOBILE_WEB_BUNDLE_RANGE_MAX_DATA_BASE64_LENGTH,
   MOBILE_WEB_BUNDLE_RANGE_METHOD
-} from '../../../src/shared/mobile-web-bundle/bundle-range-rpc-contract'
-import {
-  MOBILE_WEB_BUNDLE_CAPABILITY,
-  MOBILE_WEB_BUNDLE_RANGE_CAPABILITY
-} from '../../../src/shared/mobile-web-bundle/mobile-web-bundle-capability'
+} from '../../../src/shared/mobile-web-bundle/bundle-rpc-contract'
 import { MOBILE_WEB_BUNDLE_MAX_ASSET_BYTES } from '../../../src/shared/mobile-web-bundle/manifest-contract'
 import { mobileWebBundleRangeRead } from './mobile-web-bundle-operations'
-import { mobileWebBundleReadMethodFor } from './mobile-web-bundle-read-method'
 
 function rangeReply(overrides: Record<string, unknown> = {}) {
   return {
@@ -72,25 +67,3 @@ describe('mobile web bundle range reply reader', () => {
     expect(mobileWebBundleRangeRead.barrier).toBe('on-settle')
   })
 })
-
-describe('which read method a host is paged with', () => {
-  const NEW_DESKTOP = [
-    'files.pathsExist',
-    MOBILE_WEB_BUNDLE_CAPABILITY,
-    MOBILE_WEB_BUNDLE_RANGE_CAPABILITY,
-    'terminal.quick-commands.v1'
-  ]
-  /** Derived, never written down: the one string removed from what the new desktop sends. */
-  const OLD_DESKTOP = NEW_DESKTOP.filter(
-    (capability) => capability !== MOBILE_WEB_BUNDLE_RANGE_CAPABILITY
-  )
-
-  it('pages a new client against a new host in ranges', () => {
-    expect(mobileWebBundleReadMethodFor(NEW_DESKTOP)).toBe('range')
-  })
-
-  it('pages a new client against an old host in chunks', () => {
-    expect(mobileWebBundleReadMethodFor(OLD_DESKTOP)).toBe('chunk')
-    expect(mobileWebBundleReadMethodFor([])).toBe('chunk')
-  })
-})

mobile/src/transport/mobile-web-bundle-read-method.ts

@@ -1,16 +0,0 @@
-import { MOBILE_WEB_BUNDLE_RANGE_CAPABILITY } from '../../../src/shared/mobile-web-bundle/mobile-web-bundle-capability'
-
-/** `range` pages 384 KiB gzipped windows; `chunk` pages the 48 KiB raw ones every bundle host serves. */
-export type MobileWebBundleReadMethod = 'range' | 'chunk'
-
-/**
- * Read off the `status.get` capabilities this connection already proved, never probed: a phone
- * calling a method an older desktop never allowlisted is told `forbidden`, not `method_not_found`,
- * so a probe would need to read an authorization code as absence. A host without the capability
- * keeps being paged in chunks, which is what it has always served.
- */
-export function mobileWebBundleReadMethodFor(
-  hostCapabilities: readonly string[]
-): MobileWebBundleReadMethod {
-  return hostCapabilities.includes(MOBILE_WEB_BUNDLE_RANGE_CAPABILITY) ? 'range' : 'chunk'
-}

mobile/src/transport/mobile-web-bundle-reply-schemas.ts

@@ -1,6 +1,8 @@
 import { z } from 'zod'
-import { MOBILE_WEB_BUNDLE_CHUNK_BYTES } from '../../../src/shared/mobile-web-bundle/bundle-rpc-contract'
-import { MOBILE_WEB_BUNDLE_RANGE_MAX_DATA_BASE64_LENGTH } from '../../../src/shared/mobile-web-bundle/bundle-range-rpc-contract'
+import {
+  MOBILE_WEB_BUNDLE_CHUNK_BYTES,
+  MOBILE_WEB_BUNDLE_RANGE_MAX_DATA_BASE64_LENGTH
+} from '../../../src/shared/mobile-web-bundle/bundle-rpc-contract'
 import {
   computeMobileWebBundleId,
   MobileWebBundleAssetPathSchema,
@@ -8,7 +10,8 @@ import {
   MOBILE_WEB_BUNDLE_MAX_ASSET_BYTES,
   MOBILE_WEB_BUNDLE_MAX_ROUTE_GRANTS,
   MOBILE_WEB_BUNDLE_MAX_ROUTES,
-  MOBILE_WEB_BUNDLE_MAX_TOTAL_BYTES
+  MOBILE_WEB_BUNDLE_MAX_TOTAL_BYTES,
+  SHA256_PATTERN
 } from '../../../src/shared/mobile-web-bundle/manifest-contract'
 
 // Hoisted, never built inside a reader: a schema constructed per parse cost 2275 ns against 156 ns
@@ -19,10 +22,6 @@ import {
 // member would turn a later optional field into a released-client break instead of the Rule 1
 // addition `docs/reference/remote-wire-compatibility.md` allows.
 
-/** Lowercase hex digest. The shared contract keeps its copy private, so this is the one place the
- *  client states the shape it accepts. */
-const SHA256_PATTERN = /^[a-f0-9]{64}$/
-
 /** Base64 of one chunk, bounded by the same arithmetic as `skill-upload-session-contract.ts`, so a
  *  host that overshoots is refused at the boundary instead of at reassembly. */
 const MAX_DATA_BASE64_LENGTH = Math.ceil(MOBILE_WEB_BUNDLE_CHUNK_BYTES / 3) * 4 + 8