test(tools): pin the U+200C tail/head split; qualify the identifier-equivalence measurement

The docstring names ZWNJ/ZWJ as a skew instance but nothing checked the
predicate's tail-position accept branch; this is its first test, and it
also covers camelCase's Tool-prefix branch for a head that is
XID_Continue but not XID_Start.

The equivalence sentence pinned its evidence to Node 22.23.1 against
CPython 3.9.6 without saying the samples sit inside those two versions'
shared tables, next to five named characters where that same pair
diverges.

packages/core/tools/tests/py-types.spec.ts

@@ -466,6 +466,35 @@ describe('renderToolsSdkPy', () => {
     expect(text).not.toContain('field:')
   })
 
+  it('keeps U+200C in a name tail while rejecting it at a name head, per the two XID properties', () => {
+    // ZWNJ carries `XID_Continue` and not `XID_Start`, so the predicate splits
+    // on position: bare in a tail, subscripted at a head. Both verdicts are
+    // stable across the supported engines — the property arrives in Unicode
+    // 15.1 and the floor (Node 22.19.0, Unicode 16.0) is past it.
+    //
+    // The interpreter side is where this one skews, and it is the same skew the
+    // docstring's four other characters record, reached in a tail position
+    // instead of at a head: CPython reads XID_Continue out of the
+    // `DerivedCoreProperties.txt` of the UCD it was built against (13.0.0 on
+    // 3.9.6 and 15.0.0 on 3.12.13 both lack the row, and `'a‌b'.isidentifier()`
+    // is False on both, measured), so the field emitted bare here needs an
+    // interpreter with 15.1 tables or newer.
+    const of = (name: string): ToolSdkSchema => ({
+      name,
+      description: `Tool ${name}.`,
+      parameters: { type: 'object', additionalProperties: false, properties: { 'a‌b': { type: 'string' } } },
+      output: { type: 'string' },
+    })
+    const text = renderToolsSdkPy([of('ping'), of('‌b')])
+    expect(text).toContain('async def ping(self, args: PingArgs) -> str:')
+    expect(text).toContain('    a‌b: NotRequired[str]')
+    // A head that is XID_Continue but not XID_Start takes the subscript path,
+    // and `camelCase` prefixes `Tool` to make the class name start legally.
+    expect(text).toContain('# tools["‌b"](args: Tool‌bArgs) -> str')
+    expect(text).toContain('class Tool‌bArgs(TypedDict):')
+    expect(text).not.toContain('async def ‌b')
+  })
+
   it('subscripts a tool name that NFKC-normalizes to something else, while declaring a plain Unicode one', () => {
     // Same split at the tool-name site: `路径` becomes an `async def`, the
     // ligature name cannot, because `async def find` would define `find`. The