codemode: tool discovery helper documented three ways; only bare search(input) works on 1.18.21 — README's 'never fails' claim is false

Summary

Three opencode surfaces describe the Code Mode tool-discovery helper with three
different invocation forms, and on opencode 1.18.21 only one of them works:

Impact: models following either of the two documented namespaced forms hit a hard
UnknownTool failure with no actionable suggestion, and can misdiagnose the
scaffolding as broken rather than mis-invoked.

The README also states the search tool is "always registered … so a speculative
tools.$codemode.search call never fails as an unknown tool" — that claim is
false on this build (reproduction below).

Environment

• opencode version: 1.18.21 (Homebrew, release)
• OS: Darwin 27.0.0 arm64 (macOS)
• Terminal: iTerm.app (xterm-256color, truecolor)
• Shell: /bin/zsh
• Install/channel: release
• Active plugins: @dietrichgebert/ponytail, @ljw1004/opencode-trace

Reproduction

Deterministic within a single session; each form was tested in its own execute()
sandbox against the same partial catalog (~91 tools across 6 namespaces):

1. Start a session with Code Mode active and a partial inline catalog.
2. In one execute() sandbox, run tools.$codemode.search({ query: "jira", limit: 2 })
   — the README's documented form.
   → Unknown tool '$codemode.search'.
3. In another sandbox, run Object.keys(tools) → lists the 6 MCP namespaces with
   no $codemode namespace present, confirming it is not registered there at all.
4. In another sandbox, run bare search({ query: "jira add comment", limit: 2 })
   → succeeds immediately, returning exact catalog paths such as
   tools["mcp-atlassian-jira"].jira_add_comment.

Similarly tools.search({ query }) → Unknown tool 'search'.

Expected Behavior

1. One canonical invocation form should hold everywhere: scaffold, README, and the
   Workflow/Rules guidance baked into every execute() description.
2. The UnknownTool suggestions for these paths should point at whichever form is
   real (e.g. "use bare search({ query })"), instead of failing circularly —
   notably, upstream tool-runtime.ts already attaches helpful suggestions to
   UnknownTool errors; this build surfaced none for either failed form.
3. If the intended contract is tools.$codemode.search, then per the README it
   should never raise UnknownTool; if the intended contract is a bare global, the
   README/workflow text should not advertise $codemode.search, and the "never
   fails" sentence needs correcting or version-scoping.

Actual Behavior

• The generated scaffold on 1.18.21 documents discovery as a bare global
  search(input: {...}), separate from the ## Available tools section whose
  entries are all tools.*.
• The codemode README (and current dev/v2 source in tool-runtime.ts) document the
  same helper as tools.$codemode.search(...), always registered under a reserved
  namespace, and Object.keys(tools) on other builds reportedly includes
  $codemode.
• On 1.18.21 neither namespaced form resolves, and Object.keys(tools) shows no
  $codemode; only the bare global exists. Any model following the README or the
  convention it learned from the catalog fails and gets an unhelpful error.

Related but distinct prior reports:

• #40611 — nested-runtime collision where a separate MCP server's internal
  tools.search() resolved against the outer Code Mode catalog (fixed via
  codemode: false). This report concerns a single runtime with no second server.
• #41389 — catalog-listed MCP tools failing when invoked outside execute. This
  report concerns the discovery helper itself, inside execute.

Additional Context

Suggested fix directions (any one suffices):

1. Register the discovery tool in both places inside the sandbox (alias bare
   search ↔ tools.$codemode.search), so all three documented forms work.
2. Version-scope/correct the README's "never fails as an unknown tool" claim, or
   restore registration under $codemode.
3. Make the two failing paths' UnknownTool suggestions name the working form.

Local mitigation on this machine: a version-stamped instruction block in
~/.config/opencode/AGENTS.md documenting that discovery is a bare global on
1.18.21 and everything else lives under tools.*.