fix(code): fix truncated diff preview

[adboio]

problem

diff viewer is a little broken - mostly because sometimes the tool output is too large, causing the "diff preview content" to be something like this:

<persisted-output>
Output too large (110.7KB). Full output saved to: /Users/adambowker/Library/Application Support/@posthog/posthog-code-dev/claude/projects/-Users-adambowker-posthog/019ce8a1-8438-7365-af52-3e0d8a594eb2/tool-results/toolu_019XVYxMKKxpPvfecMUzFEwj.txt  
Preview (first 2KB):  
import './EditSurvey.scss'  
import { DndContext } from '@dnd-kit/core'  
import { SortableContext, verticalListSortingStrategy } from '@dnd-kit/sortable'  
import { BindLogic, useActions, useMountedLogic, useValues } from 'kea'  
...
</persisted-output>

when this happens, 1) it looks bad, 2) the stats are computed incorrectly as +0 -0 , and 3) just means you can’t actually view the diff

also, the diff sometimes doesn't work if it's a delete-only, because we only check newText when rendering the diff

changes

1. updates EditToolView to check oldText || newText to determine if there is a diff, instead of only newText
2. updates toolInfoFromToolUse to build the diff by:
   1. first, check file content cache exists and is valid (old text exists in the content)
   2. if missing or not valid, attempt to read the file contents from disk
   3. if both of those fail, fall back to rendering fragment diff only, no context lines

[adboio]

• feat(code): remove auto-submit from slash commands, fix search #1237
• chore(code): add permissions-related events #1236
• fix(code): fix truncated diff preview #1235 👈 (View in Graphite)
• feat(code): improve pasted text UX #1234
• feat(code): pause timer when awaiting user input #1233
• main

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[charlesvien]

Merge activity

• Mar 14, 7:26 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Mar 14, 7:32 PM UTC: Graphite rebased this pull request as part of a merge.
• Mar 14, 7:36 PM UTC: @charlesvien merged this pull request with Graphite.