Land the changed files and diff reads as their own Git History branch

[Defmon3]

Seen on: component/git-history

What it fixes

After the first two server PRs, a client can page commits and refs but cannot see what a commit changed. This piece adds two reads: a page of the files one commit changed, and the diff for the commit or for one of its files, with the patch size capped and a flag when it was cut.

Why we need it

It is PR 3 of the series in the Git History series issue (#8), the last server piece. It completes the five reads the web side needs, so every later PR is UI only.

How to fix it

Cut a fresh branch on top of the second server piece carrying the changed-files read with its cursor, the diff read with its size cap, their contracts, their permission scope, and their tests. The PR description states the end state from the series issue. Deferred: everything under the web app.

[Defmon3]

Technical appendix: Land the changed files and diff reads as their own Git History branch

Investigated on branch component/git-history at commit 821fc7f, base upstream/main at a6797b3.

Findings: what the piece contains today

• packages/contracts/src/git.ts: the commit files input and result (with nextCursor and a required capped), and the commit diff input and result with a truncated flag. packages/contracts/src/rpc.ts: vcs.listCommitFiles and vcs.getCommitDiff.
• apps/server/src/vcs/GitVcsDriverCore.ts: listCommitFiles (about 90 lines), getCommitDiff (about 120), parseGitCommitChangedFiles, the commit files snapshot map with storeCommitFilesSnapshot, newCommitFilesCursor, deleteCommitFilesSnapshot, and the limits GIT_COMMIT_FILES_MAX_FILES (2,000), GIT_COMMIT_FILES_DEFAULT_LIMIT (100), GIT_COMMIT_FILES_SNAPSHOT_MAX_SESSIONS (64), GIT_COMMIT_FILES_SNAPSHOT_TTL_MS (2 minutes), GIT_COMMIT_FILES_MAX_OUTPUT_BYTES (512 KB).
• apps/server/src/ws.ts and apps/server/src/auth/RpcAuthorization.ts: handlers and read scope.

Size: about 300 source lines plus tests.

Findings: behavior established by reading

• Both reads take only a GitCommitHash, which the contract pins to hex, so no user text reaches git as a ref.
• getCommitDiff caps the patch bytes and sets the truncated flag instead of failing.

The problem

Observed: the file and diff reads exist only inside a branch that also carries the other reads and the UI.

Once done: a branch on top of the second server piece adds the two reads with their tests, and a caller sees a cursor for long file lists and a truncated flag for large diffs.