fix(snapshot): respect gitignore for previously tracked files

Files previously tracked in the snapshot that were later added to .gitignore
were still being included in patches. This happened because:

1. diff-files returns tracked files regardless of gitignore status
2. git add was re-adding all files including those now ignored
3. patch() and diffFull() output wasn't filtering out gitignored files

The fix:
- In add(): Use git check-ignore --no-index to identify newly-ignored files
  (even if they're tracked in source git) and remove them from the snapshot
  index with git rm --cached
- In patch(): Filter out gitignored files from the diff output using
  git check-ignore --no-index
- In diffFull(): Filter out gitignored files from the diff output

Tests added:
1. files tracked in snapshot but now gitignored are filtered out
   Uses a.txt (from bootstrap) to test files already in git

2. gitignore updated between track calls filters from diff
   Tests that gitignore changes between two track() calls
   properly filter from diffFull results

Fixes issue where files like .android-sdk were re-added to snapshots
even after being added to .gitignore.

packages/opencode/src/snapshot/index.ts

@@ -177,8 +177,39 @@ export namespace Snapshot {
             const all = Array.from(new Set([...tracked, ...untracked]))
             if (!all.length) return
 
+            // Filter out files that are now gitignored even if previously tracked
+            // Files may have been tracked before being gitignored, so we need to check
+            // against the source project's current gitignore rules
+            // Use --no-index to check purely against patterns (ignoring whether file is tracked)
+            const checkArgs = [
+              ...quote,
+              "--git-dir",
+              path.join(state.worktree, ".git"),
+              "--work-tree",
+              state.worktree,
+              "check-ignore",
+              "--no-index",
+              "--",
+              ...all,
+            ]
+            const check = yield* git(checkArgs, { cwd: state.directory })
+            const ignored =
+              check.code === 0 ? new Set(check.text.trim().split("\n").filter(Boolean)) : new Set<string>()
+            const filtered = all.filter((item) => !ignored.has(item))
+
+            // Remove newly-ignored files from snapshot index to prevent re-adding
+            if (ignored.size > 0) {
+              const ignoredFiles = Array.from(ignored)
+              log.info("removing gitignored files from snapshot", { count: ignoredFiles.length })
+              yield* git([...cfg, ...args(["rm", "--cached", "-f", "--", ...ignoredFiles])], {
+                cwd: state.directory,
+              })
+            }
+
+            if (!filtered.length) return
+
             const large = (yield* Effect.all(
-              all.map((item) =>
+              filtered.map((item) =>
                 fs
                   .stat(path.join(state.directory, item))
                   .pipe(Effect.catch(() => Effect.void))
@@ -259,14 +290,39 @@ export namespace Snapshot {
                   log.warn("failed to get diff", { hash, exitCode: result.code })
                   return { hash, files: [] }
                 }
+                const files = result.text
+                  .trim()
+                  .split("\n")
+                  .map((x) => x.trim())
+                  .filter(Boolean)
+
+                // Filter out files that are now gitignored
+                if (files.length > 0) {
+                  const checkArgs = [
+                    ...quote,
+                    "--git-dir",
+                    path.join(state.worktree, ".git"),
+                    "--work-tree",
+                    state.worktree,
+                    "check-ignore",
+                    "--no-index",
+                    "--",
+                    ...files,
+                  ]
+                  const check = yield* git(checkArgs, { cwd: state.directory })
+                  if (check.code === 0) {
+                    const ignored = new Set(check.text.trim().split("\n").filter(Boolean))
+                    const filtered = files.filter((item) => !ignored.has(item))
+                    return {
+                      hash,
+                      files: filtered.map((x) => path.join(state.worktree, x).replaceAll("\\", "/")),
+                    }
+                  }
+                }
+
                 return {
                   hash,
-                  files: result.text
-                    .trim()
-                    .split("\n")
-                    .map((x) => x.trim())
-                    .filter(Boolean)
-                    .map((x) => path.join(state.worktree, x).replaceAll("\\", "/")),
+                  files: files.map((x) => path.join(state.worktree, x).replaceAll("\\", "/")),
                 }
               }),
             )
@@ -616,6 +672,30 @@ export namespace Snapshot {
                       } satisfies Row,
                     ]
                   })
+
+                // Filter out files that are now gitignored
+                if (rows.length > 0) {
+                  const files = rows.map((r) => r.file)
+                  const checkArgs = [
+                    ...quote,
+                    "--git-dir",
+                    path.join(state.worktree, ".git"),
+                    "--work-tree",
+                    state.worktree,
+                    "check-ignore",
+                    "--no-index",
+                    "--",
+                    ...files,
+                  ]
+                  const check = yield* git(checkArgs, { cwd: state.directory })
+                  if (check.code === 0) {
+                    const ignored = new Set(check.text.trim().split("\n").filter(Boolean))
+                    const filtered = rows.filter((r) => !ignored.has(r.file))
+                    rows.length = 0
+                    rows.push(...filtered)
+                  }
+                }
+
                 const step = 100
                 const patch = (file: string, before: string, after: string) =>
                   formatPatch(structuredPatch(file, file, before, after, "", "", { context: Number.MAX_SAFE_INTEGER }))

packages/opencode/test/snapshot/snapshot.test.ts

@@ -511,6 +511,49 @@ test("circular symlinks", async () => {
   })
 })
 
+test("source project gitignore is respected - ignored files are not snapshotted", async () => {
+  await using tmp = await tmpdir({
+    git: true,
+    init: async (dir) => {
+      // Create gitignore BEFORE any tracking
+      await Filesystem.write(`${dir}/.gitignore`, "*.ignored\nbuild/\nnode_modules/\n")
+      await Filesystem.write(`${dir}/tracked.txt`, "tracked content")
+      await Filesystem.write(`${dir}/ignored.ignored`, "ignored content")
+      await $`mkdir -p ${dir}/build`.quiet()
+      await Filesystem.write(`${dir}/build/output.js`, "build output")
+      await Filesystem.write(`${dir}/normal.js`, "normal js")
+      await $`git add .`.cwd(dir).quiet()
+      await $`git commit -m init`.cwd(dir).quiet()
+    },
+  })
+
+  await Instance.provide({
+    directory: tmp.path,
+    fn: async () => {
+      const before = await Snapshot.track()
+      expect(before).toBeTruthy()
+
+      // Modify tracked files and create new ones - some ignored, some not
+      await Filesystem.write(`${tmp.path}/tracked.txt`, "modified tracked")
+      await Filesystem.write(`${tmp.path}/new.ignored`, "new ignored")
+      await Filesystem.write(`${tmp.path}/new-tracked.txt`, "new tracked")
+      await Filesystem.write(`${tmp.path}/build/new-build.js`, "new build file")
+
+      const patch = await Snapshot.patch(before!)
+
+      // Modified and new tracked files should be in snapshot
+      expect(patch.files).toContain(fwd(tmp.path, "new-tracked.txt"))
+      expect(patch.files).toContain(fwd(tmp.path, "tracked.txt"))
+
+      // Ignored files should NOT be in snapshot
+      expect(patch.files).not.toContain(fwd(tmp.path, "new.ignored"))
+      expect(patch.files).not.toContain(fwd(tmp.path, "ignored.ignored"))
+      expect(patch.files).not.toContain(fwd(tmp.path, "build/output.js"))
+      expect(patch.files).not.toContain(fwd(tmp.path, "build/new-build.js"))
+    },
+  })
+})
+
 test("gitignore changes", async () => {
   await using tmp = await bootstrap()
   await Instance.provide({
@@ -535,6 +578,67 @@ test("gitignore changes", async () => {
   })
 })
 
+test("files tracked in snapshot but now gitignored are filtered out", async () => {
+  await using tmp = await bootstrap()
+  await Instance.provide({
+    directory: tmp.path,
+    fn: async () => {
+      // a.txt is already committed from bootstrap - track it in snapshot
+      const before = await Snapshot.track()
+      expect(before).toBeTruthy()
+
+      // Modify a.txt (so it appears in diff-files)
+      await Filesystem.write(`${tmp.path}/a.txt`, "modified content")
+
+      // Now add gitignore that would exclude a.txt
+      await Filesystem.write(`${tmp.path}/.gitignore`, "a.txt\n")
+
+      // Also modify b.txt which is not gitignored
+      await Filesystem.write(`${tmp.path}/b.txt`, "also modified")
+
+      const patch = await Snapshot.patch(before!)
+
+      // a.txt is now gitignored and should NOT appear in patch
+      expect(patch.files).not.toContain(fwd(tmp.path, "a.txt"))
+
+      // .gitignore itself should appear (it's a new file)
+      expect(patch.files).toContain(fwd(tmp.path, ".gitignore"))
+
+      // b.txt should appear (not gitignored)
+      expect(patch.files).toContain(fwd(tmp.path, "b.txt"))
+    },
+  })
+})
+
+test("gitignore updated between track calls filters from diff", async () => {
+  await using tmp = await bootstrap()
+  await Instance.provide({
+    directory: tmp.path,
+    fn: async () => {
+      // First track - a.txt is tracked in snapshot
+      const before = await Snapshot.track()
+      expect(before).toBeTruthy()
+
+      // Modify a.txt
+      await Filesystem.write(`${tmp.path}/a.txt`, "modified content")
+
+      // Now add a.txt to gitignore
+      await Filesystem.write(`${tmp.path}/.gitignore`, "a.txt\n")
+
+      // Second track - should not include a.txt even though it changed
+      const after = await Snapshot.track()
+      expect(after).toBeTruthy()
+
+      // Verify a.txt is NOT in the diff between snapshots
+      const diffs = await Snapshot.diffFull(before!, after!)
+      expect(diffs.some((x) => x.file === "a.txt")).toBe(false)
+
+      // But .gitignore should be in the diff
+      expect(diffs.some((x) => x.file === ".gitignore")).toBe(true)
+    },
+  })
+})
+
 test("git info exclude changes", async () => {
   await using tmp = await bootstrap()
   await Instance.provide({