[gemini-cli] bug(core): stripToolCallIdPrefixes drops functionResponse.parts, so images read with read_file never reach the model

## Observed symptom bug(core): stripToolCallIdPrefixes drops functionResponse.parts, so images read with read_file never reach the model When the model reads an image with `read_file` (for example a screenshot it just took of its own page), the image never reaches the model. The tool reports success, the model only receives `"Binary content provided (1 item(s))."`, and it then describes an image it never saw. Asked for the title of a screenshot whose title is "PLANET CARTOONIA", `gemini-3.8-flash` answered "CONCEPT CAR", "LITTLE HEROES" and "GLOBAL AGENT HACKATHON" in three runs. **Cause.** `stripToolCallIdPrefixes()` in `packages/core/src/core/geminiChat.ts` rebuilds every function response whose id starts with `<toolName>__`, which CLI-generated ids always do (e.g. `read_file__call_134320`), from three fields only: ## Literal error text ``` packages/core/src/core/geminiChat.ts ``` ## Environment GitHub google-gemini/gemini-cli #29589 ## Trigger / context Public GitHub report in google-gemini/gemini-cli (FRESH_7D). ## Source evidence - https://github.com/google-gemini/gemini-cli/issues/29589 (2026-10-01T13:19:27Z) — evidence_class: PRIMARY_ISSUE_REPORT — #29589 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T10:47:55.298020Z - scout_id: C98f68b0fde ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.