read_file previously hard-rejected any read whose formatted output exceeded
the ~100K char safety limit, returning an error with zero content. A file
with few but very long lines (logs, wide CSV rows, minified data) sails past
the line-count limit and then trips the char guard, so the model gets nothing
and must guess a smaller limit — wasting a full round-trip.
Now the read is trimmed to the last complete line that fits the budget and
returns the partial content plus truncated_by="bytes" and a next_offset, so
the model paginates forward instead of starting over. A single line larger
than the whole budget is clamped on a code-point boundary (never empty) and
the cursor still advances. Applies at both read paths (normal + extracted
documents).
Adapted from IronClaw's Rust dual line/byte cap to hermes's Python tool-layer
char guard, which is the single uniform chokepoint over the gutter-rendered
content for every backend.
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