feat(flow): FlowStep output_mapping, JSON-pointer input_mapping, dynamic params

[dgenio]

Implements three related FlowStep I/O wiring features that share the executor's
input-binding and output-merge machinery:

• output_mapping (Add FlowStep.output_mapping to rename and prune tool outputs before context merge #386): optional {context_key: output_key} that renames/prunes
  a tool's validated outputs before the context merge; raw outputs stay on the
  StepRecord. Honoured across linear/DAG, sync/async, resume/replay, the builder,
  serialization, the JSON schema, and compile_flow static validation. Adds
  OutputMappingError (CW-E041).
• JSON-pointer input_mapping (Support dotted-path / JSON-pointer lookups in FlowStep.input_mapping #387): an input_mapping string starting with "/"
  resolves as an RFC-6901 pointer into the nested context. Plain keys unchanged;
  misses raise InputMappingError naming the pointer. Pointer logic extracted to a
  dependency-free chainweaver._pointer module shared with contrib json_pluck so
  core never imports the optional contrib extra.
• dynamic_params (Dynamic parameter injection: hide params from LLM schema, inject at runtime (#315) #316): execute_flow/execute_flow_async accept dynamic_params,
  merged into the running context after input_schema validation (via a run-scoped
  thread-local, mirroring dry_run) so they reach every step and the final output
  without appearing in the LLM-visible input_schema. Declarative
  Flow/DAGFlow.dynamic_params records expected params.

Also wraps a pre-existing over-length line in tests/test_release_tooling.py to
keep ruff green.

https://claude.ai/code/session_019vrFkhFWxGApdEnaqdStiw

[Copilot]

Pull request overview

Adds three flow wiring capabilities to ChainWeaver’s executor “data plane” (input binding + context merge): remapping tool outputs before merge, RFC-6901 JSON-pointer lookups for nested inputs, and runtime-injected dynamic parameters that stay out of model-visible input schemas.

Changes:

• Add FlowStep.output_mapping plus executor/compiler/serialization/schema support and a new OutputMappingError (CW-E041).
• Extend FlowStep.input_mapping resolution to support RFC-6901 JSON pointers (leading /) via shared chainweaver._pointer.
• Add dynamic_params injection to execute_flow / execute_flow_async, plus declarative Flow.dynamic_params / DAGFlow.dynamic_params.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/test_step_io_wiring.py	New end-to-end tests covering pointer input mapping, output remapping, and dynamic param injection.
tests/test_release_tooling.py	Wraps an overlong assertion line to keep linting green.
tests/fixtures/public_api.json	Updates the public API fixture for OutputMappingError, Flow.dynamic_params, and FlowStep.output_mapping.
schemas/flow.schema.json	Documents and schemas dynamic_params and output_mapping, plus pointer semantics in FlowStep.input_mapping.
README.md	Adds user-facing examples for pointer input mapping, output mapping, and dynamic params injection.
docs/reference/error-table.md	Registers CW-E041 / OutputMappingError in the error table.
docs/concepts/tools-and-flows.md	Documents output_mapping semantics and dynamic_params behavior.
CHANGELOG.md	Adds Unreleased entries describing the three new wiring features and behavior change notes.
chainweaver/flow.py	Adds FlowStep.output_mapping, Flow.dynamic_params, and DAGFlow.dynamic_params with doc updates.
chainweaver/executor.py	Implements output mapping in merge/replay/resume/projection and adds JSON-pointer input resolution + dynamic params injection.
chainweaver/exceptions.py	Introduces OutputMappingError and assigns it CW-E041.
chainweaver/contrib/tools.py	Refactors contrib pointer handling to reuse chainweaver._pointer.
chainweaver/compiler.py	Adds static validation for pointer roots and output_mapping contributions + unknown output key detection.
chainweaver/builder.py	Extends FlowBuilder.step() to accept output_mapping=... and documents pointer lookup behavior.
chainweaver/_pointer.py	New shared dependency-free RFC-6901 pointer parser/resolver with structured internal error.
chainweaver/_execution/context.py	Adds apply_output_mapping() and wires it into merge_step_outputs().
chainweaver/_execution/init.py	Re-exports apply_output_mapping alongside merge_step_outputs.
chainweaver/init.py	Exports OutputMappingError in the package public surface.
AGENTS.md	Updates the repo map + tables to document output_mapping, pointers, and dynamic_params.