diff --git a/.planning/phases/01-minimal-viable-sandbox/01-CONTEXT.md b/.planning/phases/01-minimal-viable-sandbox/01-CONTEXT.md
new file mode 100644
index 0000000..eaa7f7d
--- /dev/null
+++ b/.planning/phases/01-minimal-viable-sandbox/01-CONTEXT.md
@@ -0,0 +1,88 @@
+# Phase 1: Minimal Viable Sandbox - Context
+
+**Gathered:** 2026-04-09
+**Status:** Ready for planning
+
+<domain>
+## Phase Boundary
+
+Produce a working `claudebox` command via Nix flake that launches Claude Code inside a bubblewrap sandbox with environment allowlisting, filesystem isolation, secret path hiding, and on-demand tool provisioning via comma/nix. User runs `claudebox` in any project directory and gets a fully functional Claude session with secrets invisible.
+
+</domain>
+
+<decisions>
+## Implementation Decisions
+
+### Argument Passthrough
+- **D-01:** Forward all unknown flags to `claude`. claudebox claims only its own flags (`--yes`, `--dry-run`, `--check`) and passes everything else through. No `--` separator required. `--dangerously-skip-permissions` is always injected.
+
+### nix-index Database
+- **D-02:** Use `comma-with-db` from the `nix-community/nix-index-database` flake. Self-contained — bundles the package index, no host dependency, no extra bind mount needed. DB updates when the flake input is bumped.
+
+### Environment Variables
+- **D-03:** Strict allowlist per SAND-03, plus a `CLAUDEBOX_EXTRA_ENV` escape hatch. Core allowlist always passes (HOME, PATH, TERM, EDITOR, LANG, LC_ALL, NIX_SSL_CERT_FILE, SSL_CERT_FILE, ANTHROPIC_API_KEY, USER, SHELL, XDG_RUNTIME_DIR). User can add extras at launch via `CLAUDEBOX_EXTRA_ENV="COLORTERM,NODE_OPTIONS"` — their responsibility to not leak secrets.
+- **D-04:** Sandbox-generated vars (TMPDIR=/tmp, etc.) are set via `--setenv`, never read from host.
+
+### Git Identity
+- **D-05:** Generate a minimal `.gitconfig` inside the sandbox at launch time. Reads `user.name` and `user.email` from the host's git config, writes them plus `safe.directory = *` into the sandbox's `~/.gitconfig`. No host `.gitconfig` mounted — avoids credential helper, pager, and alias breakage from missing binaries.
+
+### Claude's Discretion
+- Mount ordering strategy for CWD-under-HOME (bwrap specifics)
+- Exact tmpfs layout and /dev, /proc, /tmp setup
+- How `--clearenv` + `--setenv` are sequenced in the bwrap invocation
+- DNS resolution mount strategy (resolv.conf and its symlink targets)
+- SSL cert bundle path detection
+
+</decisions>
+
+<canonical_refs>
+## Canonical References
+
+**Downstream agents MUST read these before planning or implementing.**
+
+### Project Docs
+- `.planning/PROJECT.md` — Core value, constraints, key decisions
+- `.planning/REQUIREMENTS.md` — Full requirement list with IDs (SAND-*, TOOL-*, GIT-*, NIX-*, UX-*)
+- `.planning/ROADMAP.md` — Phase 1 success criteria and requirement mapping
+
+### Stack Research
+- `CLAUDE.md` §Technology Stack — writeShellApplication, bwrap flags, comma/nix-index, flake structure, PATH construction, testing strategy
+
+</canonical_refs>
+
+<code_context>
+## Existing Code Insights
+
+### Reusable Assets
+- None — greenfield project, only CLAUDE.md exists in the repo
+
+### Established Patterns
+- None yet — Phase 1 establishes all patterns
+
+### Integration Points
+- Nix flake as entry point (`nix run`, `nix profile install`)
+- `writeShellApplication` produces the claudebox script
+- bwrap is the sole runtime dependency for sandboxing
+
+</code_context>
+
+<specifics>
+## Specific Ideas
+
+- `CLAUDEBOX_EXTRA_ENV` is comma-separated, not space-separated
+- Git identity is read from host at launch time (not build time) so it works across machines
+- `comma-with-db` as flake input, not a nixpkgs package
+
+</specifics>
+
+<deferred>
+## Deferred Ideas
+
+None — discussion stayed within phase scope
+
+</deferred>
+
+---
+
+*Phase: 01-minimal-viable-sandbox*
+*Context gathered: 2026-04-09*
diff --git a/.planning/phases/01-minimal-viable-sandbox/01-DISCUSSION-LOG.md b/.planning/phases/01-minimal-viable-sandbox/01-DISCUSSION-LOG.md
new file mode 100644
index 0000000..04776bd
--- /dev/null
+++ b/.planning/phases/01-minimal-viable-sandbox/01-DISCUSSION-LOG.md
@@ -0,0 +1,73 @@
+# Phase 1: Minimal Viable Sandbox - Discussion Log
+
+> **Audit trail only.** Do not use as input to planning, research, or execution agents.
+> Decisions are captured in CONTEXT.md — this log preserves the alternatives considered.
+
+**Date:** 2026-04-09
+**Phase:** 01-minimal-viable-sandbox
+**Areas discussed:** Argument passthrough, nix-index database, Env edge cases, Git identity
+
+---
+
+## Argument Passthrough
+
+| Option | Description | Selected |
+|--------|-------------|----------|
+| Forward all unknown | claudebox claims --yes, --dry-run, --check; everything else passes through to claude | ✓ |
+| Explicit -- separator | claudebox args before --, claude args after -- | |
+| Pass everything through | claudebox has no flags, controlled via env vars | |
+
+**User's choice:** Forward all unknown
+**Notes:** No -- separator needed. Simple and intuitive.
+
+---
+
+## nix-index Database
+
+| Option | Description | Selected |
+|--------|-------------|----------|
+| comma-with-db | Use nix-community/nix-index-database flake, bundles the DB | ✓ |
+| Mount host ~/.cache/nix-index | Bind-mount host's nix-index DB read-only | |
+| Both — prefer host, fallback to bundled | Mount host DB if exists, otherwise comma-with-db | |
+
+**User's choice:** comma-with-db
+**Notes:** Self-contained, no host dependency.
+
+---
+
+## Env Edge Cases
+
+| Option | Description | Selected |
+|--------|-------------|----------|
+| Strict allowlist | Only SAND-03 vars, rebuild to add more | |
+| Allowlist + CLAUDEBOX_EXTRA_ENV | Core allowlist + user-specified extras via comma-separated env var | ✓ |
+| Strict + computed vars | Allowlist from host + claudebox generates its own TMPDIR, COLORTERM, etc. | |
+
+**User's choice:** Allowlist + CLAUDEBOX_EXTRA_ENV
+**Notes:** Pragmatic escape hatch for power users, user takes responsibility for not leaking secrets.
+
+---
+
+## Git Identity
+
+| Option | Description | Selected |
+|--------|-------------|----------|
+| Generate minimal .gitconfig | Create sandbox-only .gitconfig with user.name, user.email, safe.directory | ✓ |
+| Mount host .gitconfig read-only | Bind-mount host config, carries over everything including broken credential helpers | |
+| Mount + override dangerous keys | Mount host config but neutralize credential.helper and core.pager via env vars | |
+
+**User's choice:** Generate minimal .gitconfig
+**Notes:** User asked whether custom git settings matter for Claude. Conclusion: Claude uses git programmatically, doesn't need aliases/pagers/merge tools. Mounting host config risks breakage from credential helpers and pagers referencing binaries not in sandbox PATH.
+
+---
+
+## Claude's Discretion
+
+- Mount ordering, tmpfs layout, /dev /proc /tmp setup
+- --clearenv + --setenv sequencing
+- DNS resolution mount strategy
+- SSL cert bundle path detection
+
+## Deferred Ideas
+
+None