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+# compose2pod 0.1.7 — variable interpolation
+
+A patch release resolving Compose-spec `${VAR}` variable interpolation
+against the process environment. Previously, a compose file using `${VAR}`
+reached the container as the literal placeholder text — `shlex.quote`
+correctly single-quoted the value for safe script embedding, which also
+meant the shell never expanded it, so nothing in the pipeline ever
+substituted the real value. Compose files that lean on host/CI environment
+values now convert and run correctly, matching `docker compose`.
+
+## Fix
+
+- **`${VAR}`-style interpolation is resolved.** Every string leaf of the
+  compose document is checked against `os.environ` before validation: `$VAR`,
+  `${VAR}`, `${VAR:-default}`, `${VAR-default}`, `${VAR:?msg}`, `${VAR?msg}`,
+  `${VAR:+alt}`, `${VAR+alt}`, and `$$` (literal `$`) are all supported. An
+  unset `$VAR`/`${VAR}` with no default resolves to an empty string and
+  prints a warning rather than failing; `${VAR:?msg}`/`${VAR?msg}` raises a
+  clear error instead of silently defaulting.
+
+## Downstream
+
+No action needed — additive and backward compatible. A document with no
+`$`-prefixed values is unaffected; one that already relied on the previous
+literal pass-through (unlikely, since it's not useful behavior) would now see
+the resolved value instead.
+
+## Internals
+
+- `architecture/supported-subset.md` documents the supported interpolation
+  forms and the explicit non-goal: no `.env` file loading, only the caller's
+  existing environment is consulted.
+- 123 tests at 100% line coverage (enforced); `ruff select=ALL`, `ty`, and
+  `eof-fixer` clean.