fix(coding-agent): follow local schema refs in tool search and codemode summaries (#11850)

Fixes #11803.

**Problem**

`tool_search` builds a tool's search text from its parameter schema but
never followed `$ref`. MCP servers (Pydantic, FastMCP) often put nested
models in `$defs`:

```json
{ "properties": { "options": { "$ref": "#/$defs/options" } },
  "$defs": { "options": { "properties": { "mode": { "description": "reconciliation" } } } } }
```

Search text was `Inspect records options`, so
`tool_search("reconciliation")` found nothing. Durable's copy of
`tool_search` had the same gap. The codemode `resolves to` summary had
the same blind spot for output schemas: a field behind a `$ref` showed
as `structuredContent?` with no field names.

**Fix**

- pi-codemode exports its existing local JSON Pointer resolver as
`resolveSchemaRef(ref, root)`. A malformed percent escape now resolves
to nothing instead of throwing `URIError` (this also affected
`schemaToType()`).
- coding-agent and Durable `schemaText()` follow local `$ref`s. Each
referenced subschema is read once, so recursive and shared definitions
neither loop nor inflate BM25 term counts. Unreferenced `$defs` and
remote refs stay out.
- coding-agent `describeFields()`/`describeUnionFields()` resolve `$ref`
chains against the output schema root.

**Tests**

- `packages/codemode/test/declarations.test.ts`: escaped, remote,
missing, malformed refs.
- `packages/coding-agent/test/tool-search.test.ts`: refs, escaped
segments, recursion and shared definitions, unused definitions.
- `packages/coding-agent/test/suite/agent-session-codemode.test.ts`:
summary through root, field, const, and union refs.
- `packages/durable/test/tool-search.test.ts`: end-to-end load via a
ref'd description; unused definition does not match.

`npm run check` passes.

packages/coding-agent/CHANGELOG.md

@@ -38,7 +38,9 @@
 - Fixed Ctrl+P not switching to the only model in scope (or the only available model) when the active model is a different one; it showed "Only one model in scope" instead. Cycling forward from a model outside the scope now also selects the first scoped model instead of skipping it ([#11806](https://github.com/earendil-works/pi/issues/11806))
 - Fixed `/reload` and session switches leaving extension overlays on screen when an extension had more than one `ctx.ui.custom({ overlay: true })` open: only the topmost overlay was removed, and the others kept focus and input although the extension that opened them was gone. All extension overlays, including hidden ones, are now removed and disposed; pi's own overlays stay open
 - Fixed `/mcp` sign-in staying on "Connecting…" for minutes after a successful browser sign-in, with Ctrl+C doing nothing: pi waited for the browser to drop an unused connection to the OAuth callback port. The callback server now closes remaining connections when it shuts down ([#11311](https://github.com/earendil-works/pi/issues/11311))
-
+- Fixed `tool_search` and `searchTools()` not finding a tool by property names and descriptions behind a local `$ref`, as in MCP input schemas that put their models in `$defs`. Referenced definitions are read once, so recursive schemas do not loop, and definitions nothing references stay out of the search text ([#11803](https://github.com/earendil-works/pi/issues/11803))
+- Fixed the codemode `resolves to` summary of a tool leaving out field names behind a local `$ref`, for example `structuredContent?` instead of `structuredContent?: { results }` for MCP output schemas that put their models in `$defs` ([#11803](https://github.com/earendil-works/pi/issues/11803))
+- Fixed every codemode script failing with `URI malformed` when any callable tool, such as an MCP tool, had a `$ref` with a malformed percent escape (`#/$defs/%E0`) in its schema, even scripts that do not call that tool. The parameter now renders as `unknown` in the tool's declaration ([#11803](https://github.com/earendil-works/pi/issues/11803))
 
 ## [1.5.0] - 2026-11-02