Review point from keeltrace, and it is a real gap: secret redaction and
prompt omission are different contracts, and only the first one is
pattern-shaped.
redact_sensitive_text removes credentials. A provider 4xx that quotes the
request back carries the user's own prose - a paragraph about a person, a
file pulled in by an @ reference - which matches no credential pattern and
so passed through untouched into cause=. The record's stated contract is
that prompt content is not logged, and the previous commit only enforced
the half of it that a regex can see. The existing prompt test could not
catch this: its provider error does not echo the prompt, so it proves the
prompt is not logged directly, not that it cannot arrive by being quoted.
_strip_prompt_echo closes the quoted path directly. Anything the message
shares with the submitted prompt for 24 characters or more becomes
<prompt>. Shingle-set matching rather than a diff, so cost is linear in
both strings on a path that runs for every failed turn and can face an
@-expanded prompt of arbitrary size; the JSON-escaped form of the prompt is
shingled too, because a provider handing back its own request body often
hands it back escaped. The prompt is captured after @-expansion on purpose:
an injected file's contents are exactly the material an echo would carry,
and they are not in the submitted text.
Ordering is load-bearing. The strip runs after the whitespace collapse, so
a re-wrapped quote still matches, and before the length cap, so a quote
cannot survive by being cut mid-run.
What this does not claim: verbatim echo is what it stops. A paraphrase, a
summary, or a re-encoding would survive it. The alternative keeltrace
raised - log only structured provider metadata and drop the message body -
is airtight but costs the diagnosis this PR exists to enable, since the
reporter needed to tell a 402 from a crashed finalizer. Happy to switch if
maintainers prefer the stricter contract.
Tests: the non-secret sentinel keeltrace asked for (a benign phrase present
only in the prompt, echoed by the provider error, asserted absent from the
record), plus guards that a message sharing nothing with the prompt is
untouched, that an overlap below the window is not treated as an echo, that
a prompt shorter than the window cannot blank the message, that a
JSON-escaped echo is stripped, that the strip precedes the length cap, and
that whitespace shape does not hide an echo. The three that cover the new
path fail with the strip removed; the guards pass either way.
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