D362 — OpenCode 2.x gets the write-findings hook through a dedicated plugin

Decision. On OpenCode 2.x and later the cartographer-write-findings hook (D353) is a dedicated generated plugin, not the generic KB-hook plugin. It subscribes ctx.tool.hook("execute.after"), acts only when the event is completed, result.output is a string and event.tool ends in _<write tool>, pipes {tool_name, tool_response} to the hook's shim on stdin, and on exit 2 appends the stderr text to event.result.output. It never throws. SupportsWriteFindingsHook(opencode) is true only when the installed major is 2 or more; on 1.x or an unreadable version nothing is installed and a previous install is pruned like an opt-out. The subcommand accepts the <server>_<tool> tool name as well as mcp__<server>__<tool>, and reads a string holding several JSON values (the write response followed by the server's sync-state block).

Why. Probed on OpenCode 2.0.25 (#638): execute.after fires for the code-mode execute tool and for each inner MCP call, named <server>_<tool>, whose result.output is the MCP result text with the sync-state block joined on a second line. Appending to that string reaches the model and keeps the result (one write). A throw reaches it as a tool error and the agent retries the write (7 hook calls against 3), losing its content_hash, the same trap as Codex exit 2 (D361). The generic plugin cannot do this: it passes no stdin, signals by throwing, and its substring matcher never matches <server>_<tool>.

Alternatives rejected. Extending the generic plugin with a per-hook mode: it would carry a second behaviour behind one generator, for one hook. Throwing, as the generic plugin does: retry loop. A --channel for OpenCode: the plugin reads stderr on exit 2 already, and the shim stays identical to Claude's. Installing on 1.x by analogy: not probed, so declared absent.

Consequences. OpenCode 2.x machines get a new plugin file on the next sync. The plugin file's regex is built from WriteFindingsTools, so a new write tool needs no change here. A write response whose JSON the model reads is unchanged; only text is appended. OpenCode 1.x is added by a probe, not by inference.