fix: remove draft-07 outputSchema that blocks 2020-12-only clients (fixes #132)

[shoemoney]

Fixes #132

Root cause

McpServer.registerTool converts zod schemas via zod-to-json-schema / zod/v4-mini with the SDK's default target draft-7. Every tool's inputSchema and outputSchema therefore advertises

"$schema": "http://json-schema.org/draft-07/schema#"

2020-12-only validators (Ajv configured for 2020-12, Claude Cowork / Claude Desktop) reject the dialect before any network call:

Tool 'perplexity_ask' has an invalid outputSchema: JSON Schema declares an unsupported dialect ("$schema": "http://.../draft-07/schema#"). The default validator supports JSON Schema 2020-12 only

Reproduced locally on v1.2.0: tools/list returned 8/8 schemas with draft-07, rejected by a 2020-12-only Ajv. Upstream tracked at modelcontextprotocol/typescript-sdk#745 and modelcontextprotocol/typescript-sdk#2084 (fix in modelcontextprotocol/typescript-sdk#2085). Bumping the SDK to 1.30.0 and moving to zod/v4 both still emit draft-07 because no target reaches mapMiniTarget.

Fix

• Drop optional outputSchema from all 4 tools (perplexity_ask, perplexity_research, perplexity_reason, perplexity_search). outputSchema is optional in the MCP spec; omitting it restores every affected client immediately without losing runtime behavior (structuredContent is still returned). Suggested as the stopgap in All tools unusable in 2020-12-only clients: outputSchema declares draft-07 dialect #132 option 2.
• Strip $schema at the tools/list boundary for inputSchema (required, cannot be dropped) and any residual outputSchema. The emitted schemas use only type/properties/required/additionalProperties/items/enum/minimum/maximum/description, which have identical semantics under draft-07 and 2020-12, so omitting the dialect tag lets clients apply their own default (SEP-1613). Safe for these 4 tools; tuple schemas would need the full 2020-12 conversion (items -> prefixItems), not just tag removal.

Verification

• Repro script via InMemoryTransport before fix: 8/8 schemas rejected (4 tools x input+output), after fix: 0/8 rejected, outputSchema absent, inputSchema has no $schema.
• npm test — 89/89 passed (4 suites) — npm run build clean.
• No behavior change to tool execution or structuredContent shape; plugin.json/mcp.json/server.json untouched.

Future

Re-add outputSchema once the SDK emits 2020-12 by default (target draft-2020-12 reaches the converter). The kept _responseOutputSchema / _searchOutputSchema constants document the intended shape.