feat: add property-based fuzzing harness, trace minimization, and CLI (#220, #221, #222, #217)

[dgenio]

Add an active failure-discovery layer that complements ChainWeaver's existing
replay/diff/attest reproduction primitives.

• chainweaver/fuzz.py (Add property-based fuzzing harness for ChainWeaver flows #220): FlowFuzzer generates/mutates inputs from a flow's
  input_schema (or a base input), optionally injects malformed tool outputs via
  a seeded fault hook, executes the flow, and records FlowProperty violations as
  replayable ExecutionResult traces. All randomness is seeded so runs are
  reproducible; the executor stays randomness-free. Ships FlowProperty,
  FaultConfig, FuzzCase/FuzzFailure/FuzzReport, BUILTIN_PROPERTIES, and
  FuzzConfigError.
• minimize_failure (Minimize failing execution traces into smallest reproducible failure #221): delta-debugs a failing input to the smallest
  reproducer that still violates a property, re-verifying each reduction.
• chainweaver fuzz CLI (Add chainweaver fuzz command for property-based flow testing #222): --property (builtin or module:attr), --runs,
  --seed, --input/--input-file, --output-fault-prob, --minimize, --save-failures
  (redacted by default), --format. Non-zero exit on violation. Documented in
  docs/cli.md.
• RedactionPolicy.redact_step_record / redact_execution_result (Add RedactionPolicy.redact_step_record / redact_execution_result helpers #217): return
  redacted copies of StepRecord / ExecutionResult, used by the save-failures
  path. Implemented with Pydantic model_copy (the models are BaseModel with
  string-only error fields, not dataclasses carrying live exceptions).

Tests cover detection, seed determinism, fault injection, minimization,
redaction round-trips, and the full CLI exit-code contract. All four validation
commands pass; project coverage 91%.

https://claude.ai/code/session_01KQy8CtFEATMZ8rZmkepQ1Y

[github-actions]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'ChainWeaver microbenchmarks'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.25.

Benchmark suite	Current: 98a777c	Previous: 6fd70ff	Ratio
compiled_overhead_ms_n5_llm200_tool0	0.16273200003524835 ms	0.12229499998284155 ms	1.33

This comment was automatically generated by workflow using github-action-benchmark.

CC: @dgenio

[Copilot]

Pull request overview

Adds an active failure-discovery layer to ChainWeaver by introducing a deterministic, property-based fuzzing harness for flows, optional tool-output fault injection, failure minimization, and a chainweaver fuzz CLI workflow that can save replayable traces (with redaction support).

Changes:

• Adds chainweaver.fuzz with FlowFuzzer, FlowProperty, FaultConfig, result models, and minimize_failure(...) for deterministic shrinking.
• Adds chainweaver fuzz CLI command with --property, --runs/--seed, optional fault injection, optional minimization, and optional saving of (redacted) failing traces.
• Extends RedactionPolicy with trace-level helpers (redact_step_record / redact_execution_result) and adds tests + docs + public API snapshot updates for the new surface.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
tests/test_redaction.py	Adds coverage for new trace-redaction helpers on RedactionPolicy.
tests/test_fuzz.py	Adds unit tests for fuzzing determinism, violations, fault injection, and minimization.
tests/test_cli_fuzz.py	Adds CLI contract tests for chainweaver fuzz (exit codes, determinism, saving/minimizing, redaction).
tests/fixtures/public_api.json	Updates public API snapshot for newly exported fuzzing symbols.
README.md	Documents FuzzConfigError and adds an example chainweaver fuzz invocation.
docs/cli.md	Documents the new fuzz command flags, JSON output shape, and exit codes.
CHANGELOG.md	Adds unreleased changelog entries for fuzzing, minimization, CLI command, and redaction helpers.
chainweaver/log_utils.py	Adds RedactionPolicy.redact_step_record and redact_execution_result.
chainweaver/fuzz.py	Introduces the property-based fuzzing harness + minimizer implementation.
chainweaver/cli.py	Implements the chainweaver fuzz command and property resolution logic.
chainweaver/__init__.py	Exports fuzzing API via __all__.