refactor(extension): class-based command registry + modular src layout

Restructure the MV3 background worker from a monolithic core.ts/index.ts
into a class-based command architecture. Behavior is identical — the 83
registered commands dispatch byte-for-byte the same as before.

Structure
- One class per command group, each extending CommandGroup and exporting a
  `commands` map keyed by the full command id ("tabs.close"). Groups:
  Navigation, TabsMutation, TabsQuery, Groups, Windows, Dom (dom/extract/
  page), BrowserData (storage/cookies), Session (session/clients + autosave
  + lazy-tab activation), Perf (perf + jobs.status/cancel), Extension.
- CommandRegistry merges the group maps (throws on duplicate ids), routes
  background specs to JobManager and paginates array results via
  makePagedData. JobManager owns the job map + lifecycle. NativeConnection
  owns the native-port lifecycle and the inbound message router.
- index.ts is now thin wiring: JobManager -> ctx -> assembleRegistry ->
  onActivated -> NativeConnection.start().
- Infra classes live in classes/ (PascalCase, file = class name); command
  groups in commands/; shared helpers split out of core.ts into core/
  (errors, throttle, scripting, tab-helpers, group-helpers, storage); all
  types moved into types/ (json, jobs, session, tabs, messages,
  command-args) behind a barrel.

DRY cleanup
- resolveTabUrl(tabId) and assertScriptableUrl(url, action) collapse the
  tab/URL-guard boilerplate duplicated across dom.ts and browser-data.ts.
- processInBatches() centralizes the throttled, cancellable batch loop
  shared by tabs.close, group.close and tabs.merge_windows.
- captureCurrentSession() dedups the snapshot-and-signature block shared by
  session.save and the autosave path.
- DomArgs type alias replaces 21 inline ContentArgs & { tabId? } copies.
- Drop fetchTabHtml's redundant retry loop (executeScript already retries
  transient frame/tab errors), a dead tabInfo import, and two stale
  comments referencing a removed asArgs helper.

Type safety & tests
- Full noImplicitAny; no `any`/`unknown` annotations remain in src.
- JS unit-test harness using node --test + node:assert (zero new deps),
  bundled via the existing esbuild. Covers JobManager retention/lifecycle
  and the autosave listener-wiring/debounce with an in-memory chrome mock.
- The structural pytest checks track the new file homes and the centralized
  processInBatches helper.

Verification: npm run check:extension green (tsc + esbuild 84.5kb +
node --check + 18 JS tests); uv run pytest -q -> 409 passed, 105 skipped.
No version bump.

tests/test_extension_error_page_handling.py

@@ -3,16 +3,20 @@ from pathlib import Path
 ROOT = Path(__file__).resolve().parents[1]
 
 def test_extension_retries_error_page_script_injection_before_failing():
-    core = (ROOT / "extension" / "src" / "core.ts").read_text()
+    # core.ts was split into a core/ subfolder during the structure refactor:
+    # the URL/error classifiers live in core/errors.ts and the executeScript
+    # retry wrapper (which calls isTransientScriptError) lives in core/scripting.ts.
+    errors = (ROOT / "extension" / "src" / "core" / "errors.ts").read_text()
+    scripting = (ROOT / "extension" / "src" / "core" / "scripting.ts").read_text()
 
-    assert "isBrowserErrorUrl" in core
-    assert "isErrorPageScriptError" in core
-    assert "chrome-error://" in core
-    assert "edge-error://" in core
-    assert "brave-error://" in core
-    assert "about:neterror" in core
-    assert "about:certerror" in core
-    assert "isTransientScriptError(e)" in core
+    assert "isBrowserErrorUrl" in errors
+    assert "isErrorPageScriptError" in errors
+    assert "chrome-error://" in errors
+    assert "edge-error://" in errors
+    assert "brave-error://" in errors
+    assert "about:neterror" in errors
+    assert "about:certerror" in errors
+    assert "isTransientScriptError(e)" in scripting
 
 def test_read_only_dom_commands_have_error_page_fallbacks():
     dom = (ROOT / "extension" / "src" / "commands" / "dom.ts").read_text()
@@ -26,7 +30,9 @@ def test_read_only_dom_commands_have_error_page_fallbacks():
     assert "isErrorPageScriptError(e)" in dom
 
 def test_navigation_and_tabs_report_browser_error_pages():
-    tabs = (ROOT / "extension" / "src" / "commands" / "tabs.ts").read_text()
+    # tabs.watch_url (which reports tab error pages) moved into the read-only
+    # TabsQueryCommands class in tabs-query.ts during the structure refactor.
+    tabs = (ROOT / "extension" / "src" / "commands" / "tabs-query.ts").read_text()
     navigation = (ROOT / "extension" / "src" / "commands" / "navigation.ts").read_text()
 
     assert "lastUrl" in tabs
@@ -37,7 +43,12 @@ def test_navigation_and_tabs_report_browser_error_pages():
     assert "showing an error page while waiting for load" in navigation
 
 def test_large_extension_operations_yield_between_batches():
-    core = (ROOT / "extension" / "src" / "core.ts").read_text()
+    # The large-operation throttling/queue helpers moved from core.ts into
+    # core/throttle.ts when core was split into a subfolder. The slice-based
+    # batch loop (cancel-check -> batch call -> progress -> yield) was then
+    # centralized into the processInBatches() helper in core/throttle.ts, so the
+    # command modules call that instead of inlining the loop.
+    core = (ROOT / "extension" / "src" / "core" / "throttle.ts").read_text()
     tabs = (ROOT / "extension" / "src" / "commands" / "tabs.ts").read_text()
     groups = (ROOT / "extension" / "src" / "commands" / "groups.ts").read_text()
     session = (ROOT / "extension" / "src" / "commands" / "session.ts").read_text()
@@ -56,14 +67,19 @@ def test_large_extension_operations_yield_between_batches():
     assert "itemCount >= 300" in core
     assert "itemCount >= 100" in core
     assert "chrome.tabs.query({ audible: true })" in core
+    # The centralized batch loop drives cancellation + progress + throttled yield.
+    assert "processInBatches" in core
+    assert "throwIfJobCancelled(progress.job)" in core
+    assert "yieldForLargeOperation(done" in core
+    # tabs.close / tabs.merge_windows now batch via processInBatches; tabs.sort
+    # still runs its own per-item move loop with yieldForLargeOperation.
+    assert "processInBatches(toClose" in tabs
+    assert "processInBatches(ids" in tabs
     assert "yieldForLargeOperation" in tabs
-    assert "toClose.slice" in tabs
-    assert "ids.slice" in tabs
     assert "w.tabs.every" in tabs
     assert "getLargeOperationThrottle" in tabs
     assert "runLargeOperation(\"tabs.sort\"" in tabs
-    assert "yieldForLargeOperation" in groups
-    assert "tabIds.slice" in groups
+    assert "processInBatches(tabIds" in groups
     assert "getLargeOperationThrottle" in groups
     assert "runLargeOperation(\"group.close\"" in groups
     assert "yieldForLargeOperation(createdTabs.length" in session
@@ -76,35 +92,50 @@ def test_large_extension_operations_yield_between_batches():
     assert "throwIfJobCancelled" in session
     assert "updateJobProgress" in session
 
-    index = (ROOT / "extension" / "src" / "index.ts").read_text()
-    assert "BACKGROUND_COMMANDS" in index
-    assert "startBackgroundJob" in index
-    assert "persistJobs" in index
-    assert "recentJobs" in index
-    assert "jobs.status" in index
-    assert "jobs.cancel" in index
-    assert "perf.status" in index
-    assert "perf.set_profile" in index
-    assert "__background" in index
+    # The background-job machinery moved out of index.ts into the JobManager
+    # (classes/JobManager.ts), the message router (classes/NativeConnection.ts)
+    # and the command registry/groups during the class-based refactor. The
+    # behavior is identical; assert the defining patterns still exist in their
+    # new homes.
+    jobs_module = (ROOT / "extension" / "src" / "classes" / "JobManager.ts").read_text()
+    connection = (ROOT / "extension" / "src" / "classes" / "NativeConnection.ts").read_text()
+    perf = (ROOT / "extension" / "src" / "commands" / "perf.ts").read_text()
+    tabs_module = (ROOT / "extension" / "src" / "commands" / "tabs.ts").read_text()
+
+    assert "background: true" in tabs_module       # background command flag (was BACKGROUND_COMMANDS)
+    assert "persistJobs" in jobs_module
+    assert "recentJobs" in jobs_module
+    assert "jobs.status" in perf
+    assert "jobs.cancel" in perf
+    assert "perf.status" in perf
+    assert "perf.set_profile" in perf
+    assert "__background" in connection
 
 
 def test_session_autosave_is_debounced_and_non_overlapping():
-    session = (ROOT / "extension" / "src" / "commands" / "session.ts").read_text()
+    # The autosave lifecycle moved out of session.ts into a dedicated
+    # AutoSaveManager (autosave.ts) during the structure refactor; the shared
+    # snapshot/signature helpers live in session-snapshot.ts. Behavior is
+    # identical — the defining patterns just live in their new homes.
+    autosave = (ROOT / "extension" / "src" / "commands" / "autosave.ts").read_text()
+    snapshot = (ROOT / "extension" / "src" / "commands" / "session-snapshot.ts").read_text()
 
-    assert "autoSaveTimer" in session
-    assert "autoSaveInFlight" in session
-    assert "autoSavePending" in session
-    assert "scheduleAutoSave" in session
-    assert "autoSaveUpdatedHandler" in session
-    assert "saveAutoSessionIfChanged" in session
-    assert "sessionSignature" in session
-    assert "autoSaveSignature" in session
-    assert "chrome.tabs.onUpdated.addListener(autoSaveUpdatedHandler)" in session
-    assert "chrome.tabs.onCreated.addListener(autoSaveHandler)" in session
-    assert "chrome.tabs.onMoved.addListener(autoSaveHandler)" in session
-    assert "if (!(\"url\" in changeInfo)) return;" in session
-    assert "setTimeout(runAutoSave, delayMs)" in session
-    assert "clearTimeout(autoSaveTimer)" in session
+    assert "autoSaveTimer" in autosave
+    assert "autoSaveInFlight" in autosave
+    assert "autoSavePending" in autosave
+    assert "scheduleAutoSave" in autosave
+    assert "autoSaveUpdatedHandler" in autosave
+    assert "saveAutoSessionIfChanged" in autosave
+    assert "sessionSignature" in snapshot
+    assert "autoSaveSignature" in autosave
+    # AutoSaveManager binds the handlers as instance fields (this.*), so the
+    # add/removeListener references stay identity-stable across enable/disable.
+    assert "chrome.tabs.onUpdated.addListener(this.autoSaveUpdatedHandler)" in autosave
+    assert "chrome.tabs.onCreated.addListener(this.autoSaveHandler)" in autosave
+    assert "chrome.tabs.onMoved.addListener(this.autoSaveHandler)" in autosave
+    assert "if (!(\"url\" in changeInfo)) return;" in autosave
+    assert "setTimeout(() => this.runAutoSave(), delayMs)" in autosave
+    assert "clearTimeout(this.autoSaveTimer)" in autosave
 
 
 def test_cli_and_sdk_expose_gentle_restore_controls():