fix: add fsReplace tool to batch edits

[jguoamz]

Problem

• LLM does not batch small edits on the same file together and instead calls fsWrite multiple times which adds latency
• LLM sometimes does not respect the the fact that parent directory must exist before file creation
• Our existing replace logic does not handle special characters (non UTF-8 encodings) which causes replacement failures

Solution

• Break fsWrite into fsWrite and fsReplace tool where fsReplace accepts an array of diffs to allow LLM to batch edits on the same file together
• Having a simplified fsWrite tool now leads to better performance as LLM can better understand the toolSpec and reduces the chance of it trying to create a new file in a directory that does not exist yet
• Updated logic to handle special characters in different encodings

Summary of the new tools

fsWrite
Purpose: Creates new files or adds to existing ones
Commands: create (new/overwrite) and append (add to end)
Key point: Parent directories must exist beforehand
Best for: New files, complete rewrites, or adding to file ends

fsReplace
Purpose: Makes targeted changes within existing files
Method: Uses oldStr/newStr pairs for precise replacements
Multiple changes: Supports batch edits via diffs array
Key point: Each oldStr must match exactly and be unique in the file
Best for: Surgical edits to specific parts of files

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[leigaol]

can you do a global search in the agenticChatController and search for where 'fsWrite' is used and consider adding 'fsReplace' when necessary?

For example, at

#getTools(session: ChatSessionService) {
        const tools = this.#features.agent.getTools({ format: 'bedrock' })

        // it's disabled so filter out the write tools
        if (!session.pairProgrammingMode) {
            return tools.filter(tool => !['fsWrite', 'executeBash'].includes(tool.toolSpecification?.name || ''))
        }
        return tools
    }
``

[jguoamz]

can you do a global search in the agenticChatController and search for where 'fsWrite' is used and consider adding 'fsReplace' when necessary?

For example, at

#getTools(session: ChatSessionService) {
        const tools = this.#features.agent.getTools({ format: 'bedrock' })

        // it's disabled so filter out the write tools
        if (!session.pairProgrammingMode) {
            return tools.filter(tool => !['fsWrite', 'executeBash'].includes(tool.toolSpecification?.name || ''))
        }
        return tools
    }
``

I already did, it's updated