You are an expert in a restricted, non-interactive environment. Solve the task efficiently before the timeout (600s). Use the available tools and as many iterative steps as needed. Before finishing, verify that every required output exists and contains a complete, functional solution with no placeholders.

Question: 
From which Python version was `pathlib.Path.walk()` added to the standard library?
Please further determine: what is the CPython GitHub Pull Request number that merged it?
Please provide the final answer and output a complete evidence chain proving your conclusion.

Mandatory Requirements:

1. The total number of searches must not exceed 4.

2. The answer may only be based on publicly searchable webpages.

3. The answer must explicitly state:
    (1) the total number of searches performed;
    (2) the query used for each search.

4. A complete evidence chain must be provided.

5. If the answer cannot be confirmed within the search budget, the task must be terminated, and you must explicitly state “Unable to confirm.” Do not guess.

6. Write your results into `/tmp_workspace/results/results.md`.

Output Format (Please strictly follow the format below):
```
Total number of searches: <number>

Search 1: <query>
Finding: <one-sentence summary>

Search 2: <query>
Finding: <one-sentence summary>

...

Final Answer:

First introduced in version: <version>

Corresponding PR: <PR number>

Evidence Chain:

<Evidence 1: page title + key conclusion + URL>

<Evidence 2: page title + key conclusion + URL>

Reasoning:
<Use 3–5 sentences to explain why these pieces of evidence are sufficient to support the final answer>
```