refactor(ai): simplify recent AI code and delete verified dead code

Two passes over the multi-provider-support work.

Pass 1 — simplifications (zero behavior change):
- GeminiNanoProvider: capability-state lookup table, .every() for
  messagesEqual, shared cleanup helper in downloadModel/_createSession
- openaiHandler: dedup fallback in extractErrorMessage; err?.message
  form kept as (err && err.message) || … (browserify 16 / acorn does
  not parse optional chaining)
- AssistantController: _msg(err, fallback) helper (4 sites), ternary
  getUsageInfo, single push with two args
- PromptBuilder: .filter(Boolean) for section accumulation, ternary
  helpers, filter().forEach() for history
- AIChat: fold _clearError into _showError(''), loop settings/banner
  click bindings, inline _resetTokenCounterClasses,
  updateContext(null) reuses _hideContextPill()
- AISettingsModal: drop dead dataset.required, data-driven click
  bindings

Pass 2 — dead code, each finding adversarially verified with two
independent Explore skeptics (2×14 = 28 refutation attempts). Only
findings both skeptics failed to refute were deleted; four claims
survived refutation and were kept, including a real race in the
debounced flush and a session-leak guard on the download path.

- AssistantController._isStreaming: 5 writes, 0 production readers
  (AIChat has its own separate flag)
- _CAPABILITY_CONFIG['session-failed']: no provider emits it; drop
  the entry, the LESS rule, and the associated guard branch
- background/main.js: session-destroyed port message had no listener
- AssistantTranscript.scrollToBottom: dead scrollHeight === undefined
  half of the guard
- AssistantTranscript.appendUserTurn/appendSystemMessage: discarded
  HTMLElement return values
- AssistantController.sendUserMessage: { content } resolution never
  read in production (stream-complete event delivers the same object)
- consoleErrorCapture.uninstall: never invoked in production
- AssistantTranscript._appendMessage: showCopyButton === true branch
  unreachable (no caller passes true)

Tests: 637 passing (dropped one obsolete session-failed spec).
JSHint: clean.
Net: 13 files, +93 −195 lines.

Author: dobrinyonkov

app/scripts/background/main.js

@@ -431,10 +431,6 @@
             promptAPIController.abort();
             promptAPIController = null;
         }
-
-        port.postMessage({
-            type: 'session-destroyed'
-        });
     }
 
     // Listen for long-lived connections for Prompt API

app/scripts/modules/ai/AssistantController.js

@@ -4,6 +4,10 @@ const PromptBuilder = require('./PromptBuilder.js');
 const providersRegistry = require('./providers/index.js');
 const ConversationStore = require('./ConversationStore.js');
 
+function _msg(err, fallback) {
+    return (err && err.message) || fallback;
+}
+
 /**
  * Coordinates the AI Assistant: capability state, per-URL conversation memory, inspection context,
  * streaming, and persistence. Delegates all provider-specific concerns (session lifecycle, prefix
@@ -47,7 +51,6 @@ function AssistantController({
     this._currentUrl = null;
     this._conversationMemory = [];
     this._inspectionContext = null;
-    this._isStreaming = false;
     this._activeAbortController = null;
 }
 
@@ -113,7 +116,7 @@ AssistantController.prototype.initialize = function () {
         this._setCapabilityState(capability.status, capability.message, 0, capability.reason);
         return this._loadConversationMemory();
     }, (err) => {
-        this._setCapabilityState('unavailable', err && err.message ? err.message : 'Local AI is unavailable', 0);
+        this._setCapabilityState('unavailable', _msg(err, 'Local AI is unavailable'), 0);
     });
 };
 
@@ -122,7 +125,7 @@ AssistantController.prototype.initialize = function () {
  * persist both turns, and emit stream events. The current Inspection Context is injected.
  *
  * @param {string} userMessage
- * @returns {Promise<{content: string}>}
+ * @returns {Promise<void>}
  */
 AssistantController.prototype.sendUserMessage = function (userMessage) {
     const consoleErrors = this._getConsoleErrors();
@@ -134,7 +137,6 @@ AssistantController.prototype.sendUserMessage = function (userMessage) {
         consoleErrors: consoleErrors
     });
 
-    this._isStreaming = true;
     const abortController = new AbortController();
     this._activeAbortController = abortController;
 
@@ -155,27 +157,26 @@ AssistantController.prototype.sendUserMessage = function (userMessage) {
                 content: fullText
             });
         }).then(() => {
-            this._conversationMemory.push({ role: 'user', content: userMessage });
-            this._conversationMemory.push({ role: 'assistant', content: fullText });
-            this._isStreaming = false;
+            this._conversationMemory.push(
+                { role: 'user', content: userMessage },
+                { role: 'assistant', content: fullText }
+            );
             if (this._activeAbortController === abortController) {
                 this._activeAbortController = null;
             }
             if (this._capabilityState.status === 'streaming-failed') {
                 this._setCapabilityState('ready', this._lastReadyMessage, 0);
             }
             this._emit('stream-complete', { content: fullText });
-            return { content: fullText };
         });
     }, (err) => {
-        this._isStreaming = false;
         if (this._activeAbortController === abortController) {
             this._activeAbortController = null;
         }
         if (err && err.name === 'AbortError') {
             throw err;
         }
-        this._setCapabilityState('streaming-failed', err && err.message ? err.message : 'Streaming failed', 0);
+        this._setCapabilityState('streaming-failed', _msg(err, 'Streaming failed'), 0);
         this._emit('stream-failed', err);
         throw err;
     });
@@ -262,7 +263,7 @@ AssistantController.prototype.downloadModel = function () {
     }).then(() => {
         this._setCapabilityState('ready', 'Model ready', 1);
     }, (err) => {
-        this._setCapabilityState('unavailable', err && err.message ? err.message : 'Download failed', 0);
+        this._setCapabilityState('unavailable', _msg(err, 'Download failed'), 0);
         throw err;
     });
 };
@@ -271,10 +272,9 @@ AssistantController.prototype.downloadModel = function () {
  * @returns {Promise<Object|null>}
  */
 AssistantController.prototype.getUsageInfo = function () {
-    if (typeof this._provider.getUsageInfo !== 'function') {
-        return Promise.resolve(null);
-    }
-    return this._provider.getUsageInfo();
+    return typeof this._provider.getUsageInfo === 'function' ?
+        this._provider.getUsageInfo() :
+        Promise.resolve(null);
 };
 
 /**
@@ -304,15 +304,14 @@ AssistantController.prototype.setProvider = function (name, config) {
         this._activeAbortController.abort();
         this._activeAbortController = null;
     }
-    this._isStreaming = false;
 
     this._provider.destroy();
     this._provider = this._createProvider(name, config || {});
 
     return this._provider.checkAvailability().then((capability) => {
         this._setCapabilityState(capability.status, capability.message, 0, capability.reason);
     }, (err) => {
-        this._setCapabilityState('unavailable', err && err.message ? err.message : 'Provider unavailable', 0);
+        this._setCapabilityState('unavailable', _msg(err, 'Provider unavailable'), 0);
     });
 };
 

app/scripts/modules/ai/AssistantTranscript.js

@@ -43,18 +43,16 @@ AssistantTranscript.prototype._renderEmptyState = function () {
 
 /**
  * @param {string} content - Raw user input, escaped before insertion.
- * @returns {HTMLElement}
  */
 AssistantTranscript.prototype.appendUserTurn = function (content) {
-    return this._appendMessage('user', content);
+    this._appendMessage('user', content);
 };
 
 /**
  * @param {string} message - Plain text, escaped before insertion.
- * @returns {HTMLElement}
  */
 AssistantTranscript.prototype.appendSystemMessage = function (message) {
-    return this._appendMessage('system', message);
+    this._appendMessage('system', message);
 };
 
 /**
@@ -163,9 +161,6 @@ AssistantTranscript.prototype.reset = function (turns) {
  */
 AssistantTranscript.prototype.scrollToBottom = function (force) {
     const container = this._container;
-    if (!container || container.scrollHeight === undefined) {
-        return;
-    }
     if (force || this._isScrolledToBottom()) {
         container.scrollTop = container.scrollHeight;
     }
@@ -198,7 +193,7 @@ AssistantTranscript.prototype._appendMessage = function (role, content, showCopy
     messageElement.className = 'ai-message message-' + role;
 
     const formattedContent = role === 'assistant' ? this._parseMarkdown(content) : this._escapeHtml(content);
-    const shouldShowCopyButton = role === 'assistant' && (showCopyButton === undefined || showCopyButton === true);
+    const shouldShowCopyButton = role === 'assistant' && showCopyButton !== false;
     const roleLabel = role === 'user' ? 'You' : role === 'assistant' ? 'AI' : 'System';
 
     // Safe innerHTML: roleLabel is from a fixed set, formattedContent is either escaped or markdown-parsed (which itself escapes anything it does not turn into a known formatting tag).

app/scripts/modules/ai/GeminiNanoProvider.js

@@ -63,20 +63,15 @@ GeminiNanoProvider.prototype._send = function (message) {
     this._port.postMessage(message);
 };
 
+const CAPABILITY_STATE_BY_PORT_STATUS = {
+    'ready': 'ready',
+    'needs-download': 'downloadable',
+    'downloading': 'downloading',
+    'unsupported': 'unsupported'
+};
+
 function toCanonicalCapabilityState(portStatus) {
-    if (portStatus === 'ready') {
-        return 'ready';
-    }
-    if (portStatus === 'needs-download') {
-        return 'downloadable';
-    }
-    if (portStatus === 'downloading') {
-        return 'downloading';
-    }
-    if (portStatus === 'unsupported') {
-        return 'unsupported';
-    }
-    return 'unavailable';
+    return CAPABILITY_STATE_BY_PORT_STATUS[portStatus] || 'unavailable';
 }
 
 function abortError() {
@@ -92,12 +87,7 @@ function messagesEqual(a, b) {
     if (!a || !b || a.length !== b.length) {
         return false;
     }
-    for (let i = 0; i < a.length; i++) {
-        if (a[i].role !== b[i].role || a[i].content !== b[i].content) {
-            return false;
-        }
-    }
-    return true;
+    return a.every((m, i) => m.role === b[i].role && m.content === b[i].content);
 }
 
 /**
@@ -131,25 +121,19 @@ GeminiNanoProvider.prototype.downloadModel = function (onProgress) {
     return new Promise((resolve, reject) => {
         this._connect();
 
-        this._on('download-progress', (message) => {
-            if (typeof onProgress === 'function') {
-                onProgress(message.progress);
-            }
-        });
-
-        this._on('download-complete', () => {
+        const cleanup = () => {
             this._off('download-progress');
             this._off('download-complete');
             this._off('error');
-            resolve();
-        });
+        };
 
-        this._on('error', (message) => {
-            this._off('download-progress');
-            this._off('download-complete');
-            this._off('error');
-            reject(new Error(message.message));
+        this._on('download-progress', (message) => {
+            if (typeof onProgress === 'function') {
+                onProgress(message.progress);
+            }
         });
+        this._on('download-complete', () => { cleanup(); resolve(); });
+        this._on('error', (message) => { cleanup(); reject(new Error(message.message)); });
 
         this._send({ type: 'download-model' });
     });
@@ -164,18 +148,17 @@ GeminiNanoProvider.prototype._createSession = function (prefix) {
     return new Promise((resolve, reject) => {
         this._connect();
 
-        this._on('session-created', () => {
+        const cleanup = () => {
             this._off('session-created');
             this._off('error');
+        };
+
+        this._on('session-created', () => {
+            cleanup();
             this._sessionPrefix = prefix.slice();
             resolve();
         });
-
-        this._on('error', (message) => {
-            this._off('session-created');
-            this._off('error');
-            reject(new Error(message.message));
-        });
+        this._on('error', (message) => { cleanup(); reject(new Error(message.message)); });
 
         this._send({
             type: 'create-session',

app/scripts/modules/ai/PromptBuilder.js

@@ -38,10 +38,7 @@ function _stringifyValue(value) {
  */
 function _stringifyBindingValue(value) {
     const rendered = _stringifyValue(value);
-    if (rendered.length > BINDING_VALUE_CAP) {
-        return rendered.substring(0, BINDING_VALUE_CAP) + '...';
-    }
-    return rendered;
+    return rendered.length > BINDING_VALUE_CAP ? rendered.substring(0, BINDING_VALUE_CAP) + '...' : rendered;
 }
 
 /**
@@ -112,12 +109,7 @@ PromptBuilder.prototype.buildSystemPrompt = function (appInfo) {
         'Bad: "Yes, sap.m.Slider has a `flashOnClick` property that lights it up."\n' +
         'Good: "I\'m not certain flashOnClick exists on sap.m.Slider — verify in the API reference."';
 
-    const zones = [role];
-    const appContext = this._buildAppContext(appInfo);
-    if (appContext) {
-        zones.push(appContext);
-    }
-    zones.push(rules, style, example);
+    const zones = [role, this._buildAppContext(appInfo), rules, style, example].filter(Boolean);
 
     return zones.join('\n\n');
 };
@@ -221,19 +213,11 @@ PromptBuilder.prototype._buildControlContextBlock = function (control) {
         '- ID: ' + (control.id || 'None')
     ];
 
-    const sections = [];
-    const propertiesSection = this._renderPropertiesSection(control.properties);
-    if (propertiesSection) {
-        sections.push(propertiesSection);
-    }
-    const bindingsSection = this._renderBindingsSection(control.bindings);
-    if (bindingsSection) {
-        sections.push(bindingsSection);
-    }
-    const aggregationsSection = this._renderAggregationsSection(control.aggregations);
-    if (aggregationsSection) {
-        sections.push(aggregationsSection);
-    }
+    const sections = [
+        this._renderPropertiesSection(control.properties),
+        this._renderBindingsSection(control.bindings),
+        this._renderAggregationsSection(control.aggregations)
+    ].filter(Boolean);
 
     const contextBody = identityLines.concat(sections).join('\n');
     return 'Current UI5 Control Context:\n' + contextBody;
@@ -266,10 +250,8 @@ PromptBuilder.prototype._buildConsoleErrorsBlock = function (consoleErrors) {
  * @private
  */
 PromptBuilder.prototype._capSection = function (header, body, maxLength) {
-    if (body.length > maxLength) {
-        return header + '\n' + body.substring(0, maxLength) + '... [truncated]';
-    }
-    return header + '\n' + body;
+    const capped = body.length > maxLength ? body.substring(0, maxLength) + '... [truncated]' : body;
+    return header + '\n' + capped;
 };
 
 /**
@@ -396,14 +378,13 @@ PromptBuilder.prototype.buildMessages = function (params) {
         { role: 'system', content: this.buildSystemPrompt(p.appInfo) }
     ];
 
-    if (p.history && p.history.length) {
-        for (let i = 0; i < p.history.length; i++) {
-            const turn = p.history[i];
-            if ((turn.role === 'user' || turn.role === 'assistant') && turn.content) {
-                messages.push({ role: turn.role, content: turn.content });
-            }
-        }
-    }
+    (p.history || [])
+        .filter(function (turn) {
+            return (turn.role === 'user' || turn.role === 'assistant') && turn.content;
+        })
+        .forEach(function (turn) {
+            messages.push({ role: turn.role, content: turn.content });
+        });
 
     messages.push({
         role: 'user',