Fixes #572. Deletes the two one-release back-compat fallbacks that #567/#574 shipped for exactly one release (v0.12.1): - The `wp_agent_workflow_handler` first-callable-wins dispatch fallback and `register_workflow_handler()` in `agents_run_workflow_dispatch()`. Replaced with an explicit unattributed-dispatch rule: when no runtime is identifiable (no explicit `runtime` input, no registered spec `meta.runtime`), dispatch to the single registered runtime handler if exactly one is registered; zero is the existing `no_handler` WP_Error; more than one is a new `agents_run_workflow_ambiguous_runtime` WP_Error listing the registered keys. An attributed runtime (explicit or via spec meta) with no matching handler is `no_handler` — no fallback to any other registered handler. - The `wp_agent_workflow_known_step_types` and `wp_agent_workflow_step_handlers` legacy filters layered on top of `WP_Agent_Workflow_Step_Type_Registry` (runner constructor, runner `default_step_handlers()`, and `register-reconcile-workflow-branch.php`'s `agents_workflow_resolve_step_handlers()`). The registry is now the sole source for known step types and their handlers. Caller-supplied constructor `$step_handlers` still merge on top of registry defaults. `WP_Agent_Workflow_Spec_Validator::KNOWN_STEP_TYPES` is also removed — nothing in `src/` read it. The `wp_agent_workflow_run_recorder( $recorder, $runtime, $run_id )` filter is NOT touched — it is the scoped seam, not a fallback. Only the BACK-COMPAT paragraph in `agents_workflow_resolve_recorder()`'s docblock (documenting that WordPress's own "only pass declared args" mechanic lets an old zero-argument hook keep resolving every run) is removed, since that mechanic isn't going away and the paragraph read as if it would. Updates `docs/channels-workflows-operations.md` to the final (no back-compat) contract, and migrates every test that exercised the deleted filters/helper to `register_workflow_step_type()` / `register_workflow_runtime_handler()`, adding coverage for the new unattributed-dispatch rule (single runtime dispatches, two runtimes is ambiguous, zero is `no_handler`, an explicit unknown runtime is `no_handler`). Deletes the `workflow-step-type-registry-smoke.php` section that only asserted the legacy two-filter registration path. BREAKING CHANGE: `wp_agent_workflow_handler` filter and `register_workflow_handler()` are removed — register via `register_workflow_runtime_handler( string $runtime, callable $handler )` instead. `wp_agent_workflow_known_step_types` and `wp_agent_workflow_step_handlers` filters are removed — register via `WP_Agent_Workflow_Step_Type_Registry::register()` or `register_workflow_step_type()` instead. `WP_Agent_Workflow_Spec_Validator::KNOWN_STEP_TYPES` is removed — use `WP_Agent_Workflow_Step_Type_Registry::types()`. Must merge only after Automattic/intelligence#1085 (the migration this followed) is deployed. AI disclosure: AI assistance: Yes / Tool: OpenCode / Used for: implementation and tests.

Commits

Commits on Sep 28, 2026

refactor(workflows)!: delete one-release workflow dispatch/step-type fallbacks