diff --git a/.omo/evidence/task-4-tofu-core.log b/.omo/evidence/task-4-tofu-core.log
new file mode 100644
index 0000000..4a033ff
--- /dev/null
+++ b/.omo/evidence/task-4-tofu-core.log
@@ -0,0 +1,160 @@
+     Warning 
+     Warning ## Warning for package tofu ##
+     Warning 
+     Warning The following compiler flags have been specified in the package description
+     Warning file. They are handled by DUB and direct use in packages is discouraged.
+     Warning Alternatively, you can set the DFLAGS environment variable to pass custom flags
+     Warning to the compiler, or use one of the suggestions below:
+     Warning 
+     Warning warningsAsErrors: Use "buildRequirements" to control the warning level
+     Warning 
+             Generating test runner configuration 'tofu-test-application' for 'application' (executable).
+     Warning Excluding main source file src/main.d from test.
+    Starting Performing "unittest" build using /usr/bin/dmd for x86_64.
+  Up-to-date toml 1.0.0: target for configuration [library] is up to date.
+    Building tofu ~main: building configuration [tofu-test-application]
+src/tofu/config.d(125,9): Error: found `private` instead of statement
+        private @trusted void warn() {
+        ^
+src/tofu/config.d(132,1): Error: unmatched closing brace
+}
+^
+src/tofu/types.d(147,13): Error: variable name expected after type `string`, not `version`
+    string  version = "";
+            ^
+src/tofu/types.d(147,13):        `version` is a keyword, perhaps append `_` to make it an identifier
+src/tofu/types.d(147,21): Error: declaration expected, not `=`
+    string  version = "";
+                    ^
+src/tofu/types.d(159,16): Error: variable name expected after type `string`, not `version`
+    string     version      = "";
+               ^
+src/tofu/types.d(159,16):        `version` is a keyword, perhaps append `_` to make it an identifier
+src/tofu/types.d(159,29): Error: declaration expected, not `=`
+    string     version      = "";
+                            ^
+src/tofu/types.d(185,12): Error: variable name expected after type `string`, not `version`
+    string version = "";
+           ^
+src/tofu/types.d(185,12):        `version` is a keyword, perhaps append `_` to make it an identifier
+src/tofu/types.d(185,20): Error: declaration expected, not `=`
+    string version = "";
+                   ^
+src/tofu/types.d(268,16): Error: identifier or `new` expected following `.`, not `version`
+        result.version = spec[verStart .. verEnd];
+               ^
+src/tofu/types.d(326,12): Error: variable name expected after type `string`, not `version`
+    string version   = "";
+           ^
+src/tofu/types.d(326,12):        `version` is a keyword, perhaps append `_` to make it an identifier
+src/tofu/types.d(326,22): Error: declaration expected, not `=`
+    string version   = "";
+                     ^
+src/tofu/types.d(366,12): Error: variable name expected after type `string`, not `version`
+    string version   = "";
+           ^
+src/tofu/types.d(366,12):        `version` is a keyword, perhaps append `_` to make it an identifier
+src/tofu/types.d(366,22): Error: declaration expected, not `=`
+    string version   = "";
+                     ^
+src/tofu/types.d(405,18): Error: identifier or `new` expected following `.`, not `version`
+        assert(d.version == "");
+                 ^
+src/tofu/types.d(411,18): Error: identifier or `new` expected following `.`, not `version`
+        assert(d.version == "");
+                 ^
+src/tofu/types.d(422,18): Error: identifier or `new` expected following `.`, not `version`
+        assert(d.version == "2.0");
+                 ^
+src/tofu/types.d(428,18): Error: identifier or `new` expected following `.`, not `version`
+        assert(d.version == "2.0");
+                 ^
+src/tofu/types.d(434,18): Error: identifier or `new` expected following `.`, not `version`
+        assert(d.version == "2.0");
+                 ^
+src/tofu/types.d(440,18): Error: identifier or `new` expected following `.`, not `version`
+        assert(d.version == "2.0");
+                 ^
+src/tofu/types.d(446,18): Error: identifier or `new` expected following `.`, not `version`
+        assert(d.version == "2.0");
+                 ^
+error limit (20) reached, use `-verrors=0` to show all
+Error /usr/bin/dmd failed with exit code 1.
+     Warning 
+     Warning ## Warning for package tofu ##
+     Warning 
+     Warning The following compiler flags have been specified in the package description
+     Warning file. They are handled by DUB and direct use in packages is discouraged.
+     Warning Alternatively, you can set the DFLAGS environment variable to pass custom flags
+     Warning to the compiler, or use one of the suggestions below:
+     Warning 
+     Warning warningsAsErrors: Use "buildRequirements" to control the warning level
+     Warning 
+             Generating test runner configuration 'tofu-test-application' for 'application' (executable).
+     Warning Excluding main source file src/main.d from test.
+    Starting Performing "unittest" build using /usr/bin/dmd for x86_64.
+  Up-to-date toml 1.0.0: target for configuration [library] is up to date.
+    Building tofu ~main: building configuration [tofu-test-application]
+src/tofu/config.d(126,20): Error: function `fprintf` is not callable using argument types `(File, string, immutable(char)*, immutable(char)*, int)`
+            fprintf(stderr, "Warning: invalid %s '%s', using default %d\n",
+                   ^
+src/tofu/config.d(126,20):        cannot pass argument `makeGlobal()` of type `File` to parameter `shared(_IO_FILE)* stream`
+/usr/include/dlang/dmd/core/stdc/stdio.d(1347,13):        `core.stdc.stdio.fprintf(shared(_IO_FILE)* stream, scope const(char*) format, scope const ...)` declared here
+        int fprintf(FILE* stream, scope const char* format, scope const ...);
+            ^
+src/tofu/config.d(182,32): Error: `@safe` function `tofu.config.load` cannot call `@system` function `toml.toml.parseTOML`
+                doc = parseTOML(content);
+                               ^
+../../.dub/packages/toml/1.0.0/toml/src/toml/toml.d(431,14):        `toml.toml.parseTOML` is declared here
+TOMLDocument parseTOML(string data, TOMLOptions options=TOMLOptions.none) {
+             ^
+src/tofu/config.d(187,28): Error: function `fprintf` is not callable using argument types `(File, string, immutable(char)*, immutable(char)*)`
+                    fprintf(stderr, "Warning: malformed TOML config at %s: %s\n",
+                           ^
+src/tofu/config.d(187,28):        cannot pass argument `makeGlobal()` of type `File` to parameter `shared(_IO_FILE)* stream`
+/usr/include/dlang/dmd/core/stdc/stdio.d(1347,13):        `core.stdc.stdio.fprintf(shared(_IO_FILE)* stream, scope const(char*) format, scope const ...)` declared here
+        int fprintf(FILE* stream, scope const char* format, scope const ...);
+            ^
+src/tofu/config.d(194,28): Error: function `fprintf` is not callable using argument types `(File, string, immutable(char)*)`
+                    fprintf(stderr, "Warning: unreadable TOML config at %s, "
+                           ^
+src/tofu/config.d(194,28):        cannot pass argument `makeGlobal()` of type `File` to parameter `shared(_IO_FILE)* stream`
+/usr/include/dlang/dmd/core/stdc/stdio.d(1347,13):        `core.stdc.stdio.fprintf(shared(_IO_FILE)* stream, scope const(char*) format, scope const ...)` declared here
+        int fprintf(FILE* stream, scope const char* format, scope const ...);
+            ^
+Error /usr/bin/dmd failed with exit code 1.
+     Warning 
+     Warning ## Warning for package tofu ##
+     Warning 
+     Warning The following compiler flags have been specified in the package description
+     Warning file. They are handled by DUB and direct use in packages is discouraged.
+     Warning Alternatively, you can set the DFLAGS environment variable to pass custom flags
+     Warning to the compiler, or use one of the suggestions below:
+     Warning 
+     Warning warningsAsErrors: Use "buildRequirements" to control the warning level
+     Warning 
+             Generating test runner configuration 'tofu-test-application' for 'application' (executable).
+     Warning Excluding main source file src/main.d from test.
+    Starting Performing "unittest" build using /usr/bin/dmd for x86_64.
+  Up-to-date toml 1.0.0: target for configuration [library] is up to date.
+    Building tofu ~main: building configuration [tofu-test-application]
+     Linking tofu-test-application
+    Finished To force a rebuild of up-to-date targets, run again with --force
+     Running tofu-test-application 
+Warning: malformed TOML config at /tmp/tofu-test-config-bad-173904.toml: Invalid table key declaration (2:0)
+Warning: invalid TOFU_DEFAULT_JOBS 'not-a-number', using default 1
+3 modules passed unittests
+     Warning 
+     Warning ## Warning for package tofu ##
+     Warning 
+     Warning The following compiler flags have been specified in the package description
+     Warning file. They are handled by DUB and direct use in packages is discouraged.
+     Warning Alternatively, you can set the DFLAGS environment variable to pass custom flags
+     Warning to the compiler, or use one of the suggestions below:
+     Warning 
+     Warning warningsAsErrors: Use "buildRequirements" to control the warning level
+     Warning 
+    Starting Performing "debug" build using /usr/bin/dmd for x86_64.
+  Up-to-date toml 1.0.0: target for configuration [library] is up to date.
+  Up-to-date tofu ~main: target for configuration [application] is up to date.
+    Finished To force a rebuild of up-to-date targets, run again with --force
diff --git a/.omo/notepads/tofu-core/decisions.md b/.omo/notepads/tofu-core/decisions.md
new file mode 100644
index 0000000..5051fea
--- /dev/null
+++ b/.omo/notepads/tofu-core/decisions.md
@@ -0,0 +1,24 @@
+# Decisions — tofu-core
+
+Architectural choices and rationales discovered during work on this plan.
+
+_Auto-scaffolded by /start-work. Append new entries below - never overwrite._
+
+---
+
+### Task 4: `version` → `ver` rename
+`version` is a reserved keyword in D (conditional compilation). All struct fields bearing this name are renamed to `ver` — PackageIndex.ver, Recipe.ver, DepConstraint.ver, CacheManifest.ver, BinaryCheckResult.ver. This keeps the API readable while avoiding the keyword conflict. Downstream modules referencing these structs must use `.ver` for the version field.
+
+### Task 4: DepConstraint uses typed `DepOp` enum, not string op
+The Lua reference stores `op` as a string (`nil`, `">="`, `"=="`, etc.). In D we use a typed `DepOp` enum (`ge, le, eq, ne, gt, lt, none`) for type safety and exhaustive switching. The `parse` factory handles string-to-enum conversion at parse time.
+
+### Task 4: BuildPlan is a plain container — no sorting
+The plan specifies that `order()` returns entries in deps-first order *guaranteed by the caller*. The struct itself is just a container with `add()` and `order()` — no topological sort or dependency resolution. Sorting logic belongs in a later module (`tofu.resolver` or similar).
+
+### Task 4: Single exception type `TypesException`
+One exception class for the entire types module — no separate subclasses per error category. The parse failures (bad dep spec, invalid pool) all throw `TypesException` with a descriptive message. Callers catch `TypesException` for all type-parsing errors.
+
+### Task 4: Manual char scanning for dep spec parsing
+Rather than pulling in `std.regex`, the parser uses hand-written `isNameChar()` and `isWhite()` helpers with a simple position cursor. This keeps the module dependency-light (only `std.ascii`). The logic is a direct 1:1 port of the Lua reference patterns: `[A-Za-z0-9_.+-]` for names/versions, whitespace `[ \t]` for separators.
+
+---
diff --git a/src/tofu/types.d b/src/tofu/types.d
new file mode 100644
index 0000000..c4b7294
--- /dev/null
+++ b/src/tofu/types.d
@@ -0,0 +1,541 @@
+/// tofu.types — Core data structures shared across all tofu modules.
+///
+/// Pure data types with no I/O. All structs are @safe, all strings
+/// default to `""` (never null).
+module tofu.types;
+
+// ────────────────────────────────────────────────────────────
+// Exception
+// ────────────────────────────────────────────────────────────
+
+/// Single exception type for the types module.
+class TypesException : Exception
+{
+    @safe this(string msg)
+    {
+        super(msg);
+    }
+}
+
+// ────────────────────────────────────────────────────────────
+// Pool — package source pool
+// ────────────────────────────────────────────────────────────
+
+enum Pool
+{
+    binary,
+    recipes,
+    both,
+}
+
+/// Parse a pool string value.
+@safe Pool fromPoolString(string s)
+{
+    switch (s)
+    {
+    case "binary":
+        return Pool.binary;
+    case "recipes":
+        return Pool.recipes;
+    case "both":
+        return Pool.both;
+    default:
+        throw new TypesException("invalid pool value");
+    }
+}
+
+/// Return canonical string representation of a Pool.
+@safe string poolToString(Pool p)
+{
+    final switch (p)
+    {
+    case Pool.binary:
+        return "binary";
+    case Pool.recipes:
+        return "recipes";
+    case Pool.both:
+        return "both";
+    }
+}
+
+// ────────────────────────────────────────────────────────────
+// BuildSystem — known build systems
+// ────────────────────────────────────────────────────────────
+
+enum BuildSystem
+{
+    autotools,
+    cmake,
+    meson,
+    make,
+    cargo,
+    custom,
+    unknown,
+}
+
+/// Map a build-system string to the enum.  Unknown strings
+/// map to `BuildSystem.unknown` — callers decide how to handle it.
+@safe BuildSystem buildSystemFromString(string s)
+{
+    switch (s)
+    {
+    case "autotools":
+        return BuildSystem.autotools;
+    case "cmake":
+        return BuildSystem.cmake;
+    case "meson":
+        return BuildSystem.meson;
+    case "make":
+        return BuildSystem.make;
+    case "cargo":
+        return BuildSystem.cargo;
+    case "custom":
+        return BuildSystem.custom;
+    default:
+        return BuildSystem.unknown;
+    }
+}
+
+// ────────────────────────────────────────────────────────────
+// DepOp — dependency-constraint operators
+// ────────────────────────────────────────────────────────────
+
+enum DepOp
+{
+    ge,   // >=
+    le,   // <=
+    eq,   // ==  (and = normalised)
+    ne,   // ~=
+    gt,   // >
+    lt,   // <
+    none, // unconstrained
+}
+
+// ────────────────────────────────────────────────────────────
+// Source — where a package comes from in a build-plan entry
+// ────────────────────────────────────────────────────────────
+
+enum Source
+{
+    recipe,
+    binary,
+}
+
+// ────────────────────────────────────────────────────────────
+// Character helpers for dep-spec scanning
+// ────────────────────────────────────────────────────────────
+
+private @safe bool isNameChar(char c)
+{
+    return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z')
+        || (c >= '0' && c <= '9') || c == '_' || c == '.'
+        || c == '+' || c == '-';
+}
+
+private @safe bool isWhite(char c)
+{
+    return c == ' ' || c == '\t';
+}
+
+// ────────────────────────────────────────────────────────────
+// PackageIndex — index.lua entry
+// ────────────────────────────────────────────────────────────
+
+struct PackageIndex
+{
+    string  name    = "";
+    string  ver     = "";
+    string  summary = "";
+    Pool    pool    = Pool.both;
+}
+
+// ────────────────────────────────────────────────────────────
+// Recipe — .recipe file fields
+// ────────────────────────────────────────────────────────────
+
+struct Recipe
+{
+    string     name         = "";
+    string     ver          = "";
+    string     summary      = "";
+    string     url          = "";
+    string     sha256       = "";
+    string[]   deps;             // raw dep specs e.g. ["libfoo", "libbar>=2.0"]
+    BuildSystem buildSystem = BuildSystem.unknown;
+    string[]   configureArgs;    // extra configure arguments
+    string     buildScript  = ""; // required for custom build system
+    string     testCmd      = ""; // e.g. "test -f ${DESTDIR}/usr/bin/pkg"
+    string[]   files;            // committed file paths
+}
+
+// ────────────────────────────────────────────────────────────
+// DepConstraint — parsed dependency spec
+// ────────────────────────────────────────────────────────────
+
+/// A single parsed dependency constraint.
+///
+/// Examples:
+///   parse("libfoo")       → name="libfoo", op=none,   ver=""
+///   parse("libfoo>=2.0")  → name="libfoo", op=ge,     ver="2.0"
+///   parse("pcre2~=10.42") → name="pcre2",  op=ne,     ver="10.42"
+struct DepConstraint
+{
+    string name    = "";
+    DepOp  op      = DepOp.none;
+    string ver     = "";
+
+    /// Parse a single dependency specification string.
+    ///
+    /// Semantics ported from `vercmp.parse_dep` in ZETA/lib/vercmp.lua.
+    ///   - name  : `[A-Za-z0-9_.+-]+`
+    ///   - ops   : `>=` `<=` `==` `~=` `>` `<` `=`  (2-char checked first)
+    ///   - `=` normalises to `==`
+    ///   - trailing garbage after version → `TypesException`
+    ///   - empty string / no name          → `TypesException`
+    @safe static DepConstraint parse(string spec)
+    {
+        size_t pos = 0;
+
+        // ── skip leading whitespace ──
+        while (pos < spec.length && isWhite(spec[pos]))
+            pos++;
+
+        // ── extract name ──
+        size_t nameStart = pos;
+        while (pos < spec.length && isNameChar(spec[pos]))
+            pos++;
+
+        if (pos == nameStart)
+            throw new TypesException("bad dependency \"" ~ spec ~ "\"");
+
+        DepConstraint result;
+        result.name = spec[nameStart .. pos];
+
+        // ── skip whitespace after name ──
+        while (pos < spec.length && isWhite(spec[pos]))
+            pos++;
+
+        // ── unconstrained: no operator present ──
+        if (pos >= spec.length)
+            return result; // op=none, ver=""
+
+        // ── try matching an operator (2-char first, then 1-char) ──
+        string opStr;
+
+        if (pos + 1 < spec.length)
+        {
+            string two = spec[pos .. pos + 2];
+            if (two == ">=") { result.op = DepOp.ge; opStr = ">="; }
+            else if (two == "<=") { result.op = DepOp.le; opStr = "<="; }
+            else if (two == "==") { result.op = DepOp.eq; opStr = "=="; }
+            else if (two == "~=") { result.op = DepOp.ne; opStr = "~="; }
+        }
+
+        if (opStr.length == 0)
+        {
+            char c = spec[pos];
+            if (c == '>')      { result.op = DepOp.gt; opStr = ">"; }
+            else if (c == '<') { result.op = DepOp.lt; opStr = "<"; }
+            else if (c == '=') { result.op = DepOp.eq; opStr = "="; }
+        }
+
+        if (opStr.length == 0)
+        {
+            throw new TypesException(
+                "bad dependency constraint \"" ~ spec
+                ~ "\" (expected NAME OP VERSION)");
+        }
+
+        pos += opStr.length;
+
+        // ── skip whitespace after operator ──
+        while (pos < spec.length && isWhite(spec[pos]))
+            pos++;
+
+        // ── extract version ──
+        size_t verStart = pos;
+        while (pos < spec.length && isNameChar(spec[pos]))
+            pos++;
+        size_t verEnd = pos;
+
+        if (verStart == verEnd)
+        {
+            throw new TypesException(
+                "bad dependency constraint \"" ~ spec
+                ~ "\" (expected NAME OP VERSION)");
+        }
+
+        result.ver = spec[verStart .. verEnd];
+
+        // ── check for trailing garbage ──
+        while (pos < spec.length && isWhite(spec[pos]))
+            pos++;
+        if (pos < spec.length)
+        {
+            throw new TypesException(
+                "bad dependency constraint \"" ~ spec
+                ~ "\" (expected NAME OP VERSION)");
+        }
+
+        return result;
+    }
+}
+
+// ────────────────────────────────────────────────────────────
+// BuildPlanEntry / BuildPlan
+// ────────────────────────────────────────────────────────────
+
+struct BuildPlanEntry
+{
+    string name       = "";
+    string recipePath = "";
+    Source source     = Source.recipe;
+}
+
+/// Ordered set of packages to build.  Sorting/deps-first ordering
+/// is guaranteed by the caller; this is a plain container.
+struct BuildPlan
+{
+    BuildPlanEntry[] entries;
+
+    @safe void add(string name, string recipePath, Source source)
+    {
+        entries ~= BuildPlanEntry(name, recipePath, source);
+    }
+
+    /// Return entries in the order they were added (caller
+    /// must arrange deps-first ordering before calling this).
+    @safe BuildPlanEntry[] order()
+    {
+        return entries;
+    }
+
+    @safe bool isEmpty()
+    {
+        return entries.length == 0;
+    }
+}
+
+// ────────────────────────────────────────────────────────────
+// CacheManifest — cached-package metadata
+// ────────────────────────────────────────────────────────────
+
+struct CacheManifest
+{
+    string name      = "";
+    string ver       = "";
+    long   fetchedAt = 0; // unix timestamp
+}
+
+// ────────────────────────────────────────────────────────────
+// BuildFailure — single build failure record
+// ────────────────────────────────────────────────────────────
+
+struct BuildFailure
+{
+    string name   = "";
+    string reason = "";
+}
+
+// ────────────────────────────────────────────────────────────
+// BuildResult — build outcome tracker
+// ────────────────────────────────────────────────────────────
+
+struct BuildResult
+{
+    string[]       succeeded;
+    BuildFailure[] failed;
+
+    /// Return just the names of the packages that failed.
+    @safe string[] failedNames()
+    {
+        string[] names;
+        foreach (f; failed)
+            names ~= f.name;
+        return names;
+    }
+}
+
+// ────────────────────────────────────────────────────────────
+// BinaryCheckResult — pre-built binary availability
+// ────────────────────────────────────────────────────────────
+
+struct BinaryCheckResult
+{
+    bool   exists    = false;
+    string ver       = "";
+    bool   satisfies = false;
+}
+
+// ────────────────────────────────────────────────────────────
+// Unittests
+// ────────────────────────────────────────────────────────────
+
+@safe unittest
+{
+    // ── Pool parsing ──────────────────────────────────────
+    assert(fromPoolString("binary") == Pool.binary);
+    assert(fromPoolString("recipes") == Pool.recipes);
+    assert(fromPoolString("both") == Pool.both);
+
+    assert(poolToString(Pool.binary) == "binary");
+    assert(poolToString(Pool.recipes) == "recipes");
+    assert(poolToString(Pool.both) == "both");
+
+    bool caught = false;
+    try
+    {
+        fromPoolString("nope");
+        assert(false, "expected exception");
+    }
+    catch (TypesException e)
+    {
+        caught = true;
+    }
+    assert(caught, "invalid pool should throw");
+}
+
+@safe unittest
+{
+    // ── DepConstraint: unconstrained ─────────────────────
+    {
+        auto d = DepConstraint.parse("libfoo");
+        assert(d.name == "libfoo");
+        assert(d.op == DepOp.none);
+        assert(d.ver == "");
+    }
+    {
+        auto d = DepConstraint.parse("pcre2");
+        assert(d.name == "pcre2");
+        assert(d.op == DepOp.none);
+        assert(d.ver == "");
+    }
+}
+
+@safe unittest
+{
+    // ── DepConstraint: all operators ─────────────────────
+    {
+        auto d = DepConstraint.parse("libfoo>=2.0");
+        assert(d.name == "libfoo");
+        assert(d.op == DepOp.ge);
+        assert(d.ver == "2.0");
+    }
+    {
+        auto d = DepConstraint.parse("libfoo<=2.0");
+        assert(d.name == "libfoo");
+        assert(d.op == DepOp.le);
+        assert(d.ver == "2.0");
+    }
+    {
+        auto d = DepConstraint.parse("libfoo==2.0");
+        assert(d.name == "libfoo");
+        assert(d.op == DepOp.eq);
+        assert(d.ver == "2.0");
+    }
+    {
+        auto d = DepConstraint.parse("libfoo~=2.0");
+        assert(d.name == "libfoo");
+        assert(d.op == DepOp.ne);
+        assert(d.ver == "2.0");
+    }
+    {
+        auto d = DepConstraint.parse("libfoo>2.0");
+        assert(d.name == "libfoo");
+        assert(d.op == DepOp.gt);
+        assert(d.ver == "2.0");
+    }
+    {
+        auto d = DepConstraint.parse("libfoo<2.0");
+        assert(d.name == "libfoo");
+        assert(d.op == DepOp.lt);
+        assert(d.ver == "2.0");
+    }
+    {
+        // single = normalises to ==
+        auto d = DepConstraint.parse("libfoo=2.0");
+        assert(d.name == "libfoo");
+        assert(d.op == DepOp.eq);
+        assert(d.ver == "2.0");
+    }
+}
+
+@safe unittest
+{
+    // ── DepConstraint: edge cases ────────────────────────
+    // empty string → throw
+    bool caught = false;
+    try
+    {
+        DepConstraint.parse("");
+        assert(false, "expected exception");
+    }
+    catch (TypesException)
+    {
+        caught = true;
+    }
+    assert(caught, "empty string should throw");
+
+    // whitespace-only → throw
+    caught = false;
+    try
+    {
+        DepConstraint.parse("   ");
+        assert(false, "expected exception");
+    }
+    catch (TypesException)
+    {
+        caught = true;
+    }
+    assert(caught, "whitespace-only should throw");
+
+    // trailing garbage
+    caught = false;
+    try
+    {
+        DepConstraint.parse("libfoo>=2.0 extra");
+        assert(false, "expected exception");
+    }
+    catch (TypesException)
+    {
+        caught = true;
+    }
+    assert(caught, "trailing garbage should throw");
+}
+
+@safe unittest
+{
+    // ── BuildPlan ────────────────────────────────────────
+    BuildPlan bp;
+    assert(bp.isEmpty());
+
+    bp.add("mypkg", "path/to/mypkg.recipe", Source.recipe);
+    assert(!bp.isEmpty());
+
+    bp.add("libbar", "path/to/libbar.recipe", Source.recipe);
+
+    auto ordered = bp.order();
+    assert(ordered.length == 2);
+    assert(ordered[0].name == "mypkg");
+    assert(ordered[0].recipePath == "path/to/mypkg.recipe");
+    assert(ordered[0].source == Source.recipe);
+    assert(ordered[1].name == "libbar");
+    assert(ordered[1].recipePath == "path/to/libbar.recipe");
+    assert(ordered[1].source == Source.recipe);
+}
+
+@safe unittest
+{
+    // ── BuildResult.failedNames ──────────────────────────
+    BuildResult br;
+    assert(br.failedNames().length == 0);
+
+    br.failed ~= BuildFailure("foo", "compile error");
+    br.failed ~= BuildFailure("bar", "link error");
+    br.succeeded ~= "baz";
+
+    auto names = br.failedNames();
+    assert(names.length == 2);
+    assert(names[0] == "foo");
+    assert(names[1] == "bar");
+}