Add IPC contract tests for file viewer commands

Pins the wire format for viewer_open, viewer_get_lines, viewer_search_start,
viewer_search_poll, viewer_search_cancel, viewer_close. The viewer runs in a
separate Tauri window with its own capability file, and the coverage report
flagged it as having zero IPC-layer test (9/9 untested). mockIPC bypasses the
real permission gate, so this catches serde-shape drift only — not capability
config drift, which is a Rust-side concern.

Author: vdavid

apps/desktop/src/lib/ipc/viewer.test.ts

@@ -0,0 +1,171 @@
+/**
+ * IPC contract tests for the file viewer command surface (`viewer_open`,
+ * `viewer_get_lines`, `viewer_search_start`, `viewer_search_poll`,
+ * `viewer_search_cancel`, `viewer_close`).
+ *
+ * The viewer runs in a **separate Tauri window** (`viewer-*` label) with its own
+ * capability file (`src-tauri/capabilities/viewer.json`). The coverage report flagged
+ * this group as entirely untested at the IPC layer (9/9 untested) and noted that
+ * permission drift in the capability file would be invisible until a user opens the
+ * viewer. mockIPC can't simulate Tauri's permission gate (the gate is on the Rust
+ * side; the mock patches `__TAURI_INTERNALS__.invoke` *before* it gets there), but
+ * we can pin the wire format — that's the contract that drift can break independently
+ * of the permission system.
+ */
+
+import { afterEach, describe, expect, it } from 'vitest'
+
+import { commands } from '$lib/ipc/bindings'
+import type { LineChunk, SearchPollResult, ViewerOpenResult } from '$lib/ipc/bindings'
+import { clearIpcMocks, installIpcMock } from '$lib/ipc/test-helpers'
+
+afterEach(() => {
+  clearIpcMocks()
+})
+
+const initialLines: LineChunk = {
+  lines: ['line 0', 'line 1', 'line 2'],
+  firstLineNumber: 0,
+  byteOffset: 0,
+  totalLines: 3,
+  totalBytes: 21,
+}
+
+const openResult: ViewerOpenResult = {
+  sessionId: 'sess-1',
+  fileName: 'README.md',
+  totalBytes: 21,
+  totalLines: 3,
+  estimatedTotalLines: 3,
+  backendType: 'fullLoad',
+  capabilities: {
+    supportsLineSeek: true,
+    supportsByteSeek: false,
+    supportsFractionSeek: false,
+    knowsTotalLines: true,
+  },
+  initialLines,
+  isIndexing: false,
+}
+
+describe('commands.viewerOpen', () => {
+  it('invokes viewer_open with the path positional arg', async () => {
+    const ipc = installIpcMock()
+    ipc.mock('viewer_open', () => openResult)
+
+    const result = await commands.viewerOpen('/path/to/README.md')
+
+    expect(result).toEqual({ status: 'ok', data: openResult })
+    expect(ipc.lastCall('viewer_open')?.payload).toEqual({ path: '/path/to/README.md' })
+  })
+
+  it('surfaces IpcError on the error branch (timedOut: false for non-blocking errors)', async () => {
+    const ipc = installIpcMock()
+    ipc.mock('viewer_open', () => {
+      throw { message: 'File not found', timedOut: false }
+    })
+
+    const result = await commands.viewerOpen('/nope.txt')
+
+    expect(result.status).toBe('error')
+    if (result.status === 'error') {
+      expect(result.error).toEqual({ message: 'File not found', timedOut: false })
+    }
+  })
+})
+
+describe('commands.viewerGetLines', () => {
+  it('forwards sessionId, targetType, targetValue, count as camelCase payload keys', async () => {
+    const ipc = installIpcMock()
+    const chunk: LineChunk = {
+      lines: ['x'],
+      firstLineNumber: 100,
+      byteOffset: 500,
+      totalLines: null,
+      totalBytes: 1000,
+    }
+    ipc.mock('viewer_get_lines', () => chunk)
+
+    const targetType = 'byte'
+    const targetValue = 500
+    const count = 1
+    await commands.viewerGetLines('sess-1', targetType, targetValue, count)
+
+    expect(ipc.lastCall('viewer_get_lines')?.payload).toEqual({
+      sessionId: 'sess-1',
+      targetType,
+      targetValue,
+      count,
+    })
+  })
+})
+
+describe('commands.viewerSearchStart and viewerSearchPoll', () => {
+  it('search_start sends sessionId + query', async () => {
+    const ipc = installIpcMock()
+    ipc.mock('viewer_search_start', () => null)
+
+    await commands.viewerSearchStart('sess-2', 'TODO')
+
+    expect(ipc.lastCall('viewer_search_start')?.payload).toEqual({
+      sessionId: 'sess-2',
+      query: 'TODO',
+    })
+  })
+
+  it('search_poll delta protocol: sinceIndex on the wire matches the FE-tracked offset', async () => {
+    const ipc = installIpcMock()
+    const pollResult: SearchPollResult = {
+      status: 'running',
+      newMatches: [{ line: 5, column: 0, length: 4, byteOffset: 80 }],
+      totalMatchCount: 6,
+      totalBytes: 1000,
+      bytesScanned: 800,
+      matchLimitReached: false,
+    }
+    ipc.mock('viewer_search_poll', () => pollResult)
+
+    const result = await commands.viewerSearchPoll('sess-2', 5)
+
+    expect(result).toEqual({ status: 'ok', data: pollResult })
+    expect(ipc.lastCall('viewer_search_poll')?.payload).toEqual({
+      sessionId: 'sess-2',
+      sinceIndex: 5,
+    })
+  })
+
+  it('search_cancel takes only sessionId', async () => {
+    const ipc = installIpcMock()
+    ipc.mock('viewer_search_cancel', () => null)
+
+    await commands.viewerSearchCancel('sess-2')
+
+    expect(ipc.lastCall('viewer_search_cancel')?.payload).toEqual({ sessionId: 'sess-2' })
+  })
+})
+
+describe('commands.viewerClose', () => {
+  it('takes only sessionId and resolves to data: null on success', async () => {
+    const ipc = installIpcMock()
+    ipc.mock('viewer_close', () => null)
+
+    const result = await commands.viewerClose('sess-3')
+
+    expect(result).toEqual({ status: 'ok', data: null })
+    expect(ipc.lastCall('viewer_close')?.payload).toEqual({ sessionId: 'sess-3' })
+  })
+
+  it('surfaces a string error on the error branch (viewer_close uses Result<_, String>)', async () => {
+    const ipc = installIpcMock()
+    ipc.mock('viewer_close', () => {
+      throw 'session not found'
+    })
+
+    const result = await commands.viewerClose('bogus')
+
+    expect(result.status).toBe('error')
+    if (result.status === 'error') {
+      expect(result.error).toBe('session not found')
+    }
+  })
+})