feat(parser): strip leading stop-words (at, the, a, an) from noun phrase

Allows `look at lamp`, `examine the letter`, `take a key`, `take an oil lamp`.
Stop-words are only removed from the head of the noun phrase, not from
anywhere in the middle.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/engine/parser.test.ts

@@ -231,3 +231,40 @@ describe('parser — pronouns', () => {
     expect(result.kind).toBe('unknown')
   })
 })
+
+describe('stop-word stripping', () => {
+  const ctx: ParserContext = {
+    knownItems: ['lamp'],
+    knownEncounters: [],
+    visibleNouns: [{ id: 'lamp', aliases: ['lamp', 'oil lamp'] }],
+    inventoryItemIds: [],
+    lastNoun: null,
+    awaitingDisambiguation: null,
+  }
+
+  it('strips a leading "at" from the noun phrase', () => {
+    const cmd = parse('look at lamp', ctx)
+    expect(cmd).toEqual({
+      kind: 'verb-target',
+      verb: 'look',
+      target: { canonical: 'lamp', raw: 'lamp' },
+    })
+  })
+
+  it('strips a leading "the"', () => {
+    const cmd = parse('examine the lamp', ctx)
+    expect(cmd.kind).toBe('verb-target')
+  })
+
+  it('strips "a" and "an"', () => {
+    expect(parse('take a lamp', ctx).kind).toBe('verb-target')
+    expect(parse('take an oil lamp', ctx).kind).toBe('verb-target')
+  })
+
+  it('does not strip stop-words mid-phrase', () => {
+    // 'oil lamp' is the alias; 'oil at lamp' is not. Stop-words only strip from
+    // the head of the noun phrase, not anywhere in the middle.
+    const cmd = parse('take oil lamp', ctx)
+    expect(cmd.kind).toBe('verb-target')
+  })
+})

src/engine/parser.ts

@@ -59,6 +59,9 @@ const VERB_ONLY_VERBS = new Set<string>(['look', 'inventory', 'wait'])
 /** Two-word verb prefixes (e.g. "pick up X"). */
 const TWO_WORD_VERBS = ['pick up']
 
+/** Leading stop-words stripped from the noun phrase before matching. */
+const STOP_WORDS = new Set(['at', 'the', 'a', 'an'])
+
 function tokenize(input: string): string[] {
   return input.trim().toLowerCase().split(/\s+/).filter(Boolean)
 }
@@ -126,6 +129,11 @@ export function parse(rawInput: string, ctx: ParserContext): ParsedCommand {
     return { kind: 'unknown', raw: trimmed, reason: 'unknown-verb' }
   }
 
+  // Strip leading stop-words from the noun phrase (e.g. "at", "the", "a", "an").
+  while (rest.length > 0 && STOP_WORDS.has(rest[0]!)) {
+    rest = rest.slice(1)
+  }
+
   if (rest.length === 0) {
     if (VERB_ONLY_VERBS.has(verb)) {
       return { kind: 'verb-only', verb: verb as 'look' | 'inventory' | 'wait' }