chore+docs: config, agent registry, codecontext, v2.6 spec, changelog

Working-tree config/doc changes (.gitignore, CLAUDE.md, AGENTS.md removal + data/AGENTS.md, codecontext Dockerfile/shim — pre-existing) plus this session's v2-6 persistent-agent-sessions openspec proposal/design/tasks (planning only; feature unimplemented, reserves the v2.6.0 tag) and the v2.5.2 CHANGELOG entry.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

codecontext/Dockerfile

@@ -15,9 +15,12 @@ WORKDIR /build
 
 RUN apk add --no-cache git ca-certificates build-base
 
-# Build codecontext from the v3.2.1 tag.
+# Build codecontext from the boocode-ts fork (has .codecontextignore support).
+# Source is staged into the build context by the pre-build step:
+#   tar -czf codecontext/fork.tar.gz -C /opt/forks/codecontext .
 # CGO is required: codecontext binds tree-sitter via cgo.
-RUN git clone --depth=1 --branch v3.2.1 https://github.com/nmakod/codecontext.git /build/codecontext
+COPY fork.tar.gz /build/fork.tar.gz
+RUN mkdir -p /build/codecontext && tar -xzf /build/fork.tar.gz -C /build/codecontext
 WORKDIR /build/codecontext
 RUN CGO_ENABLED=1 GOOS=linux go build -o /build/codecontext-bin ./cmd/codecontext
 

codecontext/shim.go

@@ -191,7 +191,7 @@ func startChild() error {
 	// initial scan target — codecontext rebuilds the graph against whatever
 	// target_dir each call carries, so this is just a valid bootstrap path
 	// (the default "." is the alpine root and trips on transient /proc fds).
-	child = exec.Command("codecontext", "mcp", "--target=/opt/projects", "--watch=true")
+	child = exec.Command("codecontext", "mcp", "--target=/opt/projects", "--watch=true", "--respect-gitignore")
 	var err error
 	childStdin, err = child.StdinPipe()
 	if err != nil {