fix(file_tracking): use raw content hash for consistent change detection

[amitksingh1490]

Summary

Fix false positives in file change detection by using the raw content hash (ReadOutput.content_hash) directly instead of re-hashing truncated/formatted content. This ensures both the stored hash and the comparison hash are always derived from the same unprocessed file content, eliminating spurious "externally modified" notifications for files with long lines, 2000+ lines, or trailing newlines.

Problem

Files that were not modified were being reported as "externally changed." This affected both read-only and written files whenever the displayed content diverged from the raw file content.

Root Cause

The hash comparison in FileChangeDetector::detect() was inconsistent:

When	What was hashed
File first accessed (stored hash)	Raw full file content (fs_read.rs:164 — compute_hash(&full_content))
Change detection re-check	Processed content after line truncation, range limiting to 2000 lines, and .lines().join("\n") reconstruction

These two representations diverge whenever a file has:

• Any line longer than max_line_length (truncated by truncate_line)
• More than 2000 lines (range-limited by resolve_range)
• A trailing newline (stripped by .lines().join("\n"))

Fix

Changed FileChangeDetector to use ReadOutput.content_hash directly — the hash already computed from the full raw file by the read service — instead of re-hashing the processed output.content.

Before (file_tracking.rs):

let current_hash = match self.read_file_content(&file_path).await {
    Ok(content) => Some(compute_hash(&content)),  // hash of truncated content
    Err(_) => None,
};

After:

let current_hash = match self.read_file_hash(&file_path).await {
    Ok(hash) => Some(hash),  // ReadOutput.content_hash — hash of raw full file
    Err(_) => None,
};

Tests

Test	Verifies
test_read_file_with_matching_hash_not_detected	Read-only file with consistent raw hash produces no false positive
test_truncated_content_does_not_cause_false_positive	File with long lines (truncated display) matches by raw hash
test_truncated_written_file_not_false_positive	Written file with >2000 lines (range-limited display) matches by raw hash
4 existing tests	Unchanged — real modifications, unreadable files, and duplicate prevention still work

Changed Files

• crates/forge_app/src/file_tracking.rs — Use ReadOutput.content_hash directly; update mock to simulate raw vs truncated content divergence (+134 −17)