## Purpose

Define the few-shot prompting infrastructure for extraction — example folder structure, instruction template, ChatHistory assembly, and evaluation folder.

## Requirements

### Requirement: Few-shot example folder structure

The system SHALL store few-shot examples at `examples/extraction/few-shot/` with numbered subdirectories (e.g., `01/`, `02/`). Each subdirectory SHALL contain `input.html` (the example email) and `output.json` (the expected ExtractionResult JSON).

#### Scenario: Example folder layout

- **WHEN** the application starts
- **THEN** it reads example pairs from `examples/extraction/few-shot/` in numeric directory order

#### Scenario: Adding a new example

- **WHEN** a new subdirectory (e.g., `04/`) is added with `input.html` and `output.json`
- **THEN** the new example is included in the few-shot ChatHistory prefix after the next application restart

### Requirement: Extraction instruction template

The system SHALL load a fixed instruction template from `examples/extraction/instruction-template.txt` that defines the extraction task, the TradeItem schema, and the mapping rules (date parsing, leg flattening, currency mapping, breakclause defaults). This template is NOT the user-editable system prompt.

#### Scenario: Template loaded at startup

- **WHEN** the application starts
- **THEN** the instruction template is loaded from disk and used as the system message in the extraction ChatHistory

#### Scenario: Template content

- **WHEN** the instruction template is loaded
- **THEN** it contains the TradeItem field definitions, expected JSON output format, and explicit mapping rules

### Requirement: ChatHistory assembly with few-shot examples

The system SHALL provide a `FewShotService` that assembles a reusable ChatHistory prefix at startup: the instruction template as a system message, followed by alternating User (input.html) and Assistant (output.json) messages for each example. Each extraction request SHALL clone this prefix and append the real email as the final user message.

#### Scenario: ChatHistory prefix structure

- **WHEN** the service assembles the prefix with 3 examples
- **THEN** the ChatHistory contains: 1 system message + 3 user messages + 3 assistant messages (7 messages total)

#### Scenario: Prefix cached and cloned per request

- **WHEN** an extraction request arrives
- **THEN** the service clones the cached prefix (not re-reading from disk) and appends the email content as a new user message

### Requirement: Evaluation example folder

The system SHALL support an `examples/extraction/evaluation/` folder for bulk examples used in offline testing. This folder is NOT loaded at startup and NOT used in the few-shot prompt.

#### Scenario: Evaluation folder ignored at runtime

- **WHEN** the application starts
- **THEN** it does not load examples from `examples/extraction/evaluation/`