fix(opencode): stop storing full patch text in session summary diffs

[KirillDeviatka]

Issue for this PR

Fixes #32005

Related: #17622, #20990 (and earlier attempts #32410 / #33892 that were auto-closed)

Type of change

• Bug fix

What does this PR do?

SessionSummary.summarize() previously stored the full Snapshot.diffFull() result — including complete patch text — on user message.summary.diffs. That payload is written into an append-only message.updated.1 event log on every step-finish, so a multi-step turn that touches large files can grow the event table by multiple GB and OOM/Jetsam on reopen.

This change:

1. Stores only lightweight metadata (file, status, additions, deletions) in durable summaries
2. Drops common vendor/generated paths (e.g. node_modules/, .node-runtime/) from durable summaries
3. Makes SessionSummary.diff() recompute full patches on demand from snapshots (with legacy stored-metadata fallback)

Complementary to open #40821 (scope summary to session-touched files). This PR focuses on payload size, not path scoping.

How did you verify your code works?

• bun test test/session/summary-diffs.test.ts — PASS (strip patch; drop vendor/.node-runtime)

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Related PRs Found:

1. fix(session): scope changed file summary to session edits #40821 - fix(session): scope changed file summary to session edits

   • This is explicitly mentioned in the PR description as "Complementary to open fix(session): scope changed file summary to session edits #40821". It addresses a related concern (path scoping) while this PR focuses on payload size reduction.

2. fix(core): bound event log compaction #36710 - fix(core): bound event log compaction

   • Related to event log management and preventing unbounded growth, which connects to the issue of the event table growing too large.

Note: The PR description also references earlier attempts (#32410 and #33892 that were auto-closed) and the original issue #32005, which suggests this is a revisited fix for a known problem with session diff storage payload sizes.

[KirillDeviatka]

Note on overlap with #40821: that PR scopes diffFull to session-touched paths (which files); this one strips durable patch text / vendor paths (how much is stored). Complementary, same summary.ts. Happy to rebase onto #40821 once it lands.

[KirillDeviatka]

Local verification after updating onto latest dev (CI workflows still awaiting maintainer approval for first-time contributor runs):

bun test test/session/summary-diffs.test.ts   # 5 pass
bun test test/session/{summary-diffs,session,revert-compact}.test.ts  # 18+ pass previously; summary-diffs expanded
bun run typecheck   # packages/opencode — pass

Expanded summary-diffs tests now cover patch stripping, vendor/.node-runtime/dist deny, Windows separators, and a size regression asserting compacted payload stays << full-patch JSON.