Report an unreadable input, rather than tracebacking out of the CLI

[Shashankss1205]

Fixes #63. Fixes #62.

#63 — four reads that could raise a type nobody caught

command	before	after
trace/metrics/viz <directory> --json	exit 1, empty stdout, IsADirectoryError traceback	exit 2, {"ok": false, "error": "unreadable trace file: adir: Is a directory"}
trace <unreadable file>	exit 1, PermissionError traceback	exit 2, one document
run <non-UTF-8 file> --json	exit 1, UnicodeDecodeError traceback	exit 2, one document naming the codec
demo/run/plan with a binary grapharc.toml	exit 1, UnicodeDecodeError traceback	exit 2, ConfigError naming the file

Three root causes, all the same shape — a read whose failure mode the surrounding handler does not cover:

• _existing_trace (cli/main.py) tested path.exists(), and the three reader handlers catch only TraceReadError, so every other OSError went past both. It now opens the file where the failure is still reportable.
• cli/graphrun.py and cli/config.py each had read_text(encoding="utf-8") outside the except that catches their decoder. UnicodeDecodeError is a ValueError, so neither JSONDecodeError nor TOMLDecodeError was ever going to catch it.

replay/diff already handled this correctly, which is what marked the rest as an oversight rather than a decision. The config case matters most: grapharc.toml is picked up implicitly from the working directory, so a stray binary file there broke every configurable command.

#62 — plan --approve --json emitted unparseable output

The park notice printed to stdout ahead of the document, so json.load(stdout) raised. It is now silent in JSON mode (matching cli/live.py, which already guards its announce) and unchanged in text mode — a human still gets waiting for approval (up to 3s) — answer with: grapharc approve <dir>.

Tests

Six new tests, each confirmed red against the stashed pre-fix source:

• test_a_directory_where_a_trace_belongs_{is_a_report_not_a_traceback,fails_as_one_json_document}, parametrized over trace/metrics/viz
• test_run_reports_a_graph_file_that_is_not_utf8
• test_a_config_that_is_not_utf8_names_the_file
• test_plan_approve_in_json_mode_emits_one_document — asserts json.loads(stdout) succeeds and stderr is empty
• test_plan_approve_in_text_mode_still_announces_how_to_answer — a guard so silencing JSON mode cannot silence humans

Verification

pytest → 1785 passed, 12 deselected. ruff check grapharc tests → clean. No flaky timing failures in this run.

🤖 Generated with Claude Code