Lab 2 submission

submissions/lab2.md

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+# Lab 2 — Version Control Deep Dive
+
+## Task 1 — Git Object Model and Reflog Recovery
+
+### 1.1 Git Object Model
+
+I inspected the Git object chain from HEAD to a tree and then to a blob.
+
+```text
+$ git rev-parse HEAD
+9f41b7d...
+
+$ git cat-file -t HEAD
+commit
+
+$ git cat-file -p HEAD
+tree dc5bed5bbbbe3384cd66ce31edafc7afd1a77399
+...
+
+$ git cat-file -t dc5bed5bbbbe3384cd66ce31edafc7afd1a77399
+tree
+
+$ git cat-file -p dc5bed5bbbbe3384cd66ce31edafc7afd1a77399
+100644 blob 1c0a1e94b7bbbd951f456cda51af6b8484c3cee .gitignore
+100644 blob d10c04c6e7e0014f4fe883599c11747c15012d4e README.md
+040000 tree 7d0898a908e274ea809722844cdbd836f3b1c05a app
+040000 tree f4f047dd07b128eda5f899dfdaaf193f0291eaa2 labs
+040000 tree c0ac2d55cf4335df659b347df3d19d0594a06b6c lectures
+
+$ git cat-file -p HEAD:README.md
+README.md contents were successfully read from the blob referenced by the HEAD tree.
+```
+
+A commit object references a tree object. The tree describes the repository contents and contains references to blobs and other trees. A blob stores the actual contents of a file.
+
+### 1.2 Inside .git
+
+I inspected the internal Git directory using:
+
+```text
+$ ls -la .git/
+$ cat .git/HEAD
+ref: refs/heads/feature/lab2
+
+$ ls .git/refs/heads/
+feature
+main
+
+$ ls .git/objects/ | head
+```
+
+The `.git` directory contains the repository metadata and object database. `HEAD` identifies the currently checked-out branch. `refs/heads` stores local branch references, while `.git/objects` contains Git objects addressed by their hashes.
+
+### 1.3 Reflog Recovery
+
+I created two signed commits:
+
+```text
+6a791b0 wip(lab2): start
+971a7b8 wip(lab2): more progress
+```
+
+Then I deliberately removed them from the branch with:
+
+```text
+$ git reset --hard HEAD~2
+HEAD is now at 9f41b7d docs(lab7): make seed.json shipping explicit; require bonus artifacts, not logs
+```
+
+The reflog still contained the previous positions of HEAD:
+
+```text
+9f41b7d HEAD@{0}: reset: moving to HEAD~2
+971a7b8 HEAD@{1}: commit: wip(lab2): more progress
+6a791b0 HEAD@{2}: commit: wip(lab2): start
+```
+
+I recovered the lost work using:
+
+```text
+$ git reset --hard 971a7b8
+HEAD is now at 971a7b8 wip(lab2): more progress
+```
+
+After recovery, both commits were present again.
+
+The reflog keeps local records of recent reference movements, so commits that are no longer reachable from a branch can still be recovered while their objects exist. If `git gc` had run and the unreachable objects had already expired and been pruned, the commits might have been permanently removed from the object database, making recovery through the reflog impossible.
+
+## Task 2 — Tag Release and Rebase Feature
+
+### 2.1 Signed Annotated Tag
+
+I created and pushed the signed annotated tag:
+
+```text
+v0.1.0-lab2-lera
+```
+
+Verification:
+
+```text
+$ git tag -v "v0.1.0-lab2-${USER}"
+
+Lab 2 milestone — version control deep dive
+Good "git" signature
+```
+
+This confirms that the annotated milestone tag has a valid SSH signature.
+
+### 2.2 Rebase
+
+To simulate the main branch moving while I was working, I created a signed empty commit:
+
+```text
+$ git commit -S -s --allow-empty -m "docs: upstream moved while you worked"
+[main 8b4481c] docs: upstream moved while you worked
+```
+
+Before the rebase, the feature commits were based on the older history:
+
+```text
+971a7b8 wip(lab2): more progress
+6a791b0 wip(lab2): start
+```
+
+I rebased the feature branch onto `origin/main`:
+
+```text
+$ git rebase origin/main
+Successfully rebased and updated refs/heads/feature/lab2.
+```
+
+After the rebase, the commits received new hashes:
+
+```text
+2da3d1d wip(lab2): more progress
+548c88c wip(lab2): start
+8b4481c docs: upstream moved while you worked
+```
+
+I then safely updated the remote feature branch with:
+
+```text
+$ git push --force-with-lease -u origin feature/lab2
+```
+
+`merge` preserves the histories of both branches and normally creates a merge commit. `rebase` rewrites the feature commits on top of the new base, producing a cleaner linear history. Because rebase changes commit hashes, I used `--force-with-lease` instead of `--force` so Git would refuse to overwrite unexpected remote changes.
+
+## Bonus — Bisect a Real Bug
+
+I fetched the provided buggy branch and started a bisect session using the known bad HEAD and known good `v0.0.1` tag.
+
+The automated test command was:
+
+```text
+$ git bisect run sh -c 'cd app && go test ./... && go build ./...'
+```
+
+The failing test included:
+
+```text
+--- FAIL: TestStore_PersistsAcrossReload
+store_test.go:78: nextID not restored: got 1, want 2
+```
+
+Git bisect identified the first bad commit as:
+
+```text
+f285ede8611e55ac0a7d01100891c0cc775e0709
+refactor(store): simplify nextID restoration in load()
+```
+
+Bisect log:
+
+```text
+git bisect start
+# status: waiting for both 'good' and 'bad' commits
+# bad: [f0c9243b7c80ebb930a1ce7048a1d65b4c2ac493] docs(app): mention go test invocation
+git bisect bad f0c9243b7c80ebb930a1ce7048a1d65b4c2ac493
+# status: waiting for 'good' commit(s), bad commit known
+# good: [0ec87b808ae6a257a98ecea4a3c8d38a7f2c5ac7] chore(app): document versioning scheme (bisect fixture baseline)
+git bisect good 0ec87b808ae6a257a98ecea4a3c8d38a7f2c5ac7
+# bad: [f285ede8611e55ac0a7d01100891c0cc775e0709] refactor(store): simplify nextID restoration in load()
+git bisect bad f285ede8611e55ac0a7d01100891c0cc775e0709
+# good: [cb89bb9ee2ee5010b166061447eaca3ae0da2378] docs(store): comment the load() decode step
+git bisect good cb89bb9ee2ee5010b166061447eaca3ae0da2378
+# first bad commit: [f285ede8611e55ac0a7d01100891c0cc775e0709] refactor(store): simplify nextID restoration in load()
+```
+
+Git bisect uses binary search. At every step it approximately halves the remaining range of candidate commits. Therefore, instead of checking all N commits one by one, it needs approximately log2(N) test steps. This makes it much faster for locating a regression in a long commit history.
+
+Finally, I returned the repository to its original state with:
+
+```text
+$ git bisect reset
+```