[MODEL] "Succeeded but empty" never triggers suspicion — HTTP 200 + [] propagated silently for days (271-incident retro, 2/5)

Context

From a 90-day retrospective of 271 logged incidents building two production SaaS apps with Claude Code (each record has root cause + prevention + detection channel). This is a recurring pattern report; sibling reports from the same dataset are linked at the bottom.

Type of Behavior Issue

Claude made incorrect assumptions about my project (specifically: that success-shaped responses are trustworthy).

What Happened

When an upstream dependency fails politely — HTTP 200 with an empty array — Claude (and the pipelines it writes) treat it as a valid result:

• Our scraping vendor, when blocked by the target site, returns success+empty. Five pipeline layers each reported "normal" while the product silently produced nothing for days. Every alert Claude had designed hung off catch blocks — and this failure never enters a catch. Our logged wording: "all alerting hangs off catch — which is no alerting at all."
• A separate fetch-window bug silently discarded 2/3 of candidates. Same signature: nothing thrown, nothing logged, output just quietly shrank.

When asked to investigate "no data" symptoms, Claude's default hypothesis was "there is genuinely no data," not "the source may be failing politely."

Expected Behavior

In data-pipeline contexts, empty-success from an external dependency should be treated as a hypothesis to investigate, not a result to propagate. Concretely:

1. When writing pipeline code, default to recording why a result was empty (quota / blocked / genuinely none) and flagging consecutive-empty streaks.
2. When verifying its own work, Claude Code could surface "this verification returned 0 rows/items" as a distinct signal instead of letting it read as a pass.

Reproducibility

Pattern-level; at least 3 major incidents in 90 days, one costing days of silent production downtime.

Model / Version / Platform

Opus (most sessions; some Sonnet) · Claude Code 2.1.235 · Anthropic API · macOS

Impact

High — silent product downtime plus real money burned on paid API calls that returned nothing.