fix(eval-assist F2): validate skill/tool names against provider charset

/diff-review finding: register() and the constructor accepted skill names,
tool names, and metaToolName outside `^[a-zA-Z0-9_-]+$`. Since the skill name
prefixes its tools (name_tool), an operator name with a disallowed char (e.g.
a dot → my.skill_checkpoint) passed registration but would be REJECTED by
OpenAI/Anthropic at generate time — the exact defect class the F2 POC caught
for the separator, reintroducible via operator-supplied names. Now fails fast
at registration/construction with a ValidationError. Test added.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hamr0

src/skills.js

@@ -38,6 +38,12 @@ const { ValidationError, ToolError } = require('./errors');
 
 const META_NAME = 'skill_use';
 
+// Provider-safe identifier charset. OpenAI enforces `^[a-zA-Z0-9_-]+$` on tool names and Anthropic the
+// same shape (the POC, poc/f2-skill-thunk.mjs, proved a dot is rejected at generate time). Skill names and
+// bare tool names must satisfy this so the prefixed result — joined by `_`, itself in the set — is accepted
+// by every provider. Validating at register() fails fast, instead of surfacing as a mid-run provider error.
+const SAFE_NAME = /^[a-zA-Z0-9_-]+$/;
+
 class SkillRegistry {
   /**
    * @param {Object} [options]
@@ -56,6 +62,9 @@ class SkillRegistry {
     /** @type {Set<string>} externally-reserved names (native/MCP) for collision detection */
     this._reserved = new Set(options.reserved || []);
     this.metaToolName = options.metaToolName || META_NAME;
+    if (!SAFE_NAME.test(this.metaToolName)) {
+      throw new ValidationError(`[SkillRegistry] meta-tool name "${this.metaToolName}" must match ${SAFE_NAME} (provider tool-name charset).`);
+    }
     if (this._reserved.has(this.metaToolName)) {
       throw new ValidationError(`[SkillRegistry] meta-tool name "${this.metaToolName}" collides with a reserved tool name.`);
     }
@@ -79,6 +88,9 @@ class SkillRegistry {
     if (typeof name !== 'string' || !name) {
       throw new ValidationError(`[SkillRegistry] skill name must be a non-empty string (got ${JSON.stringify(name)}).`);
     }
+    if (!SAFE_NAME.test(name)) {
+      throw new ValidationError(`[SkillRegistry] skill name "${name}" must match ${SAFE_NAME} — it prefixes tool names, which providers reject outside that charset (e.g. a dot breaks OpenAI/Anthropic).`);
+    }
     if (this._skills.has(name)) {
       throw new ValidationError(`[SkillRegistry] duplicate skill name "${name}".`);
     }
@@ -104,6 +116,9 @@ class SkillRegistry {
       if (typeof tool.execute !== 'function') {
         throw new ValidationError(`[SkillRegistry] skill "${name}" tool "${tool.name}" is missing an execute() function.`);
       }
+      if (!SAFE_NAME.test(tool.name)) {
+        throw new ValidationError(`[SkillRegistry] skill "${name}" tool name "${tool.name}" must match ${SAFE_NAME} (provider tool-name charset).`);
+      }
       const fullName = `${name}_${tool.name}`;
       if (seenThisSkill.has(fullName)) {
         throw new ValidationError(`[SkillRegistry] skill "${name}" defines "${tool.name}" twice.`);

test/skills.test.js

@@ -74,6 +74,19 @@ describe('SkillRegistry — registration & catalog', () => {
     );
   });
 
+  it('rejects a skill name or tool name outside the provider-safe charset (fail-fast, not mid-run)', () => {
+    const skills = new SkillRegistry();
+    // A dot in the skill name → prefixed tool name breaks OpenAI/Anthropic at generate time; reject early.
+    assert.throws(() => skills.register({ name: 'my.skill', description: 'd', instructions: 'i', tools: [] }), ValidationError);
+    // A dot in a bare tool name has the same effect.
+    assert.throws(
+      () => skills.register({ name: 'ok', description: 'd', instructions: 'i', tools: [mkTool('bad.name')] }),
+      ValidationError,
+    );
+    // An unsafe meta-tool name is rejected at construction.
+    assert.throws(() => new SkillRegistry({ metaToolName: 'skill.use' }), ValidationError);
+  });
+
   it('rejects a missing description or instructions', () => {
     const skills = new SkillRegistry();
     assert.throws(() => skills.register({ name: 's', instructions: 'i', tools: [] }), ValidationError);