Add dispatch trigger for workflow-to-workflow handoff

[whme]

What

Adds a new dispatch trigger type so one running workflow can start another triggered workflow with a payload and a pre-populated trigger-context/ directory. This is the data channel polling triggers already use, now available to programmatic handoff between workflows.

This is the otter-core half of the @otter <command> Gerrit entrypoint rework; the marketplace half (the otter-dispatch workflow that uses otter dispatch for kind = workflow commands) lives in a companion PR in checkmk-claude-marketplace.

Changes

• TriggerEvent.inline_context — (filename, contents) pairs materialized into trigger-context/ in run_once, beside the existing polling pending_context path. Plain file names only (path-traversal guarded).
• TriggerDef::Dispatch + new triggers/dispatch.rs — a per-workflow inbox registry (DispatchRegistry); DispatchTrigger forwards inbox messages as trigger events. Queueing and one-run-at-a-time are reused from the existing run_triggered loop.
• DaemonCommand::Dispatch + handler, threaded through WorkflowManager::dispatch().
• CLI: otter dispatch <workflow> [--payload <str>] [--context-file <name=path>]… [--context-dir <dir>].
• Docs/example: a Dispatch trigger section in USAGE.md and an examples/dispatch-handler package.

Notes

• The target workflow must be running (its engine registers the inbox on start) and use trigger.type = "dispatch". Dispatching to a stopped or non-dispatch workflow returns a clean error.
• Backward compatible: TriggerEvent and DaemonCommand additions use serde defaults; existing trigger constructors set inline_context: None.

Testing

• triggers::dispatch unit test (inbox → trigger event with inline context).
• engine integration test: run_once writes inline_context into trigger-context/, skips traversal entries.
• workflow_manager integration test: start → dispatch → a run executes with the handed-over context.
• Full otter-core suite green except pre-existing git ssh-signing env failures in workspace_pool/git tests (unrelated). cargo clippy clean.

🤖 Generated with Claude Code

[whme]

This is the data channel polling triggers already use, now available to programmatic handoff between workflows.

I think we should migrate the polling triggers to use the dispatch trigger if possible to showcase the new architecture with existing workflows.

[Copilot]

Pull request overview

Adds a new dispatch trigger to enable workflow-to-workflow (and CLI-to-workflow) handoff by sending a payload plus inline context files that are materialized into trigger-context/ before steps run.

Changes:

• Introduces TriggerDef::Dispatch plus a new DispatchTrigger/registry for routing inbox messages into trigger events.
• Extends TriggerEvent with inline_context and updates Engine::run_once() to write these files into trigger-context/ with path-traversal protection.
• Adds otter dispatch CLI + daemon plumbing, plus documentation and an example workflow.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
USAGE.md	Documents the new dispatch trigger and CLI usage.
examples/dispatch-handler/workflow.toml	Adds a minimal dispatch-triggered example workflow.
examples/dispatch-handler/README.md	Adds usage instructions for the dispatch example.
crates/otter-tui/src/panels/right_panel.rs	Displays dispatch as a trigger type in the TUI.
crates/otter-core/src/workflow_manager.rs	Adds dispatch registry wiring and a dispatch() entrypoint.
crates/otter-core/src/workflow_manager_tests.rs	Adds an integration-ish test ensuring dispatch runs write inline context.
crates/otter-core/src/types.rs	Adds TriggerDef::Dispatch, DaemonCommand::Dispatch, and TriggerEvent.inline_context.
crates/otter-core/src/triggers/polling.rs	Initializes inline_context to None for polling events.
crates/otter-core/src/triggers/oneshot.rs	Initializes inline_context to None for oneshot events.
crates/otter-core/src/triggers/mod.rs	Registers the new dispatch trigger module and build path.
crates/otter-core/src/triggers/manual.rs	Initializes inline_context to None for manual events.
crates/otter-core/src/triggers/dispatch.rs	Implements the dispatch inbox trigger + unit test.
crates/otter-core/src/engine.rs	Plumbs dispatch registry into trigger construction; materializes inline_context into trigger-context/.
crates/otter-core/src/engine_tests.rs	Adds coverage for inline context materialization + traversal skipping.
crates/otter-cli/src/main.rs	Adds otter dispatch command and context-file collection logic.
crates/otter-cli/src/daemon.rs	Handles DaemonCommand::Dispatch by calling WorkflowManager::dispatch().

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[whme]

@whme on migrating polling triggers onto the dispatch trigger: agreed it'd be a nice showcase, but I'd keep it out of this PR. The two aren't quite substitutable — polling owns the seen-hash dedup, interval loop, and context_command execution, whereas dispatch is a passive inbox with the context handed in pre-built. A migration would mean factoring the polling loop into a thing that dispatches into the workflow's inbox, which is a worthwhile refactor but a separate change with its own tests. I've addressed the five inline review comments in a84e774. Want me to open a follow-up issue to track the polling→dispatch unification?