fix: Capture systemPrompt in Strands agent model span input

.agents/skills/e2e-tests/SKILL.md

@@ -61,6 +61,7 @@ Cassettes mock provider HTTP responses (OpenAI, Anthropic, ...) so external-prov
 - Keep reusable logic in `e2e/helpers/`. Keep one-off fixtures and scenario-specific files inside the scenario directory.
 - Snapshot stable contracts, not raw noise. Use `normalizeForSnapshot(...)` before inline snapshots and `formatJsonFileSnapshot(...)` plus file snapshots for larger payloads or version matrices.
 - For span-tree snapshots, use `matchSpanTreeSnapshot(...)`. It writes and asserts paired `.span-tree.json` and `.span-tree.txt` files from the same normalized span tree. The JSON file is the structural contract that is easiest to parse mechanically; the TXT file is the ASCII tree that is easiest to review by eye. Keep them in sync by updating both through the e2e update/record commands, and never hand-edit only one side of the pair.
+- For tracing-instrumentation span-tree snapshots, always capture `input`, `output`, `metadata`, `context`, `error`, and `metrics`. Normalize volatile values within these fields, but do not omit a field or selectively filter its semantic contents to reduce snapshot size or noise.
 - When a scenario family already has `assertions.ts`, keep version- or provider-specific test setup in `scenario.test.ts` and reuse the shared assertions file.
 - Keep the CI e2e summary up to date. If a scenario version matrix or `variantKey` changes, update `e2e/config/pr-comment-scenarios.json` in the same change and follow the established pattern used by other versioned scenarios: one summary row per version, not separate wrapped/auto rows unless that pattern already exists for the scenario family.
 - Run new or updated scenarios three times in a row before considering snapshots stable.

.changeset/capture-strands-system-prompt.md

@@ -0,0 +1,5 @@
+---
+"braintrust": patch
+---
+
+fix: Capture systemPrompt in Strands agent model span input