proxy: add debug logging to matrix solver decisions

Add set name, DSL expression, and eviction cost to SolveResult and
log solver decisions in ProxyRequest for troubleshooting.

- Add DSL field to ExpandedSet, populated during ValidateMatrix
- Add SetName, DSL, TotalCost to SolveResult
- Log eviction, cold start, and already-running cases via proxyLogger

config-schema.json

@@ -319,6 +319,41 @@
             },
             "description": "A dictionary of group settings. Provides advanced controls over model swapping behaviour. Model IDs must be defined in models. A model can only be a member of one group. Behaviour controlled via swap, exclusive, persistent."
         },
+        "matrix": {
+            "type": "object",
+            "description": "Solver-based alternative to groups. Declares valid combinations of concurrent models. The solver minimizes eviction cost when swapping. A config must use either groups or matrix, not both.",
+            "required": [
+                "sets"
+            ],
+            "properties": {
+                "map": {
+                    "type": "object",
+                    "description": "Short names for models. Keys must be alphanumeric, 1-8 characters, and must not collide with model names. All sets and evict_costs must use these IDs.",
+                    "additionalProperties": {
+                        "type": "string"
+                    },
+                    "propertyNames": {
+                        "pattern": "^[a-zA-Z0-9]{1,8}$"
+                    }
+                },
+                "evict_costs": {
+                    "type": "object",
+                    "description": "Relative cost of evicting a running model. Models not listed default to 1. Values must be positive integers.",
+                    "additionalProperties": {
+                        "type": "integer",
+                        "minimum": 1
+                    }
+                },
+                "sets": {
+                    "type": "object",
+                    "description": "Named sets of concurrent model combinations. Values are DSL strings using & (AND), | (OR), () (grouping), and +ref (inline another set). Definition order is used for tie-breaking.",
+                    "additionalProperties": {
+                        "type": "string"
+                    }
+                }
+            },
+            "additionalProperties": false
+        },
         "hooks": {
             "type": "object",
             "properties": {

config.example.yaml

@@ -393,6 +393,80 @@ groups:
       - "forever-modelB"
       - "forever-modelc"
 
+# =============================================================================
+# matrix: solver-based alternative to groups
+# =============================================================================
+#
+# A config must use either groups or matrix, not both.
+#
+# The matrix declares valid combinations of models that can run concurrently.
+# When a model is requested, the solver finds the cheapest way to make it
+# available by evicting as few (and least costly) running models as possible.
+#
+# Solver behavior:
+#   1. Request arrives for model X
+#   2. If X is already running, forward immediately. Done.
+#   3. Find all sets containing X
+#   4. For each candidate set, compute cost: sum of evict_costs for
+#      every running model NOT in that set
+#   5. Pick lowest cost candidate. Ties broken by definition order.
+#   6. Evict what needs to stop. Start X. Forward request.
+#
+# Subset semantics: a set [a, b, c] means any subset is valid.
+# Only the requested model is started — others are not preloaded.
+#
+# A model not appearing in any set can only run alone.
+#
+matrix:
+  # map: short names for models (alphanumeric, 1-8 chars)
+  # - required for sets and evict_costs settings
+  # - each entry is a short name to a model ID
+  # - used to keep set DSL logic short and easier to read
+  map:
+    g: gemma-model
+    q: qwen-model
+    m: mistral-model
+    v: voxtral-model
+    e: reranker-model
+    L: llama-70B
+    sd: stable-diffusion
+
+  # evict_costs: relative cost of losing a running model (default: 1)
+  evict_costs:
+    v: 50        # vllm backend, slow cold start
+    L: 30        # 70B weights, slow to load
+
+  # sets: named sets of concurrent model combinations
+  # Values are DSL strings with operators:
+  #   &     AND (models run together)
+  #   |     OR  (alternatives)
+  #   ()    grouping
+  #   +ref  inline another set's expression
+  #
+  # Expansion examples:
+  #   "L"                  → [L]
+  #   "a & b"              → [a, b]
+  #   "a | b"              → [a], [b]
+  #   "(a | b) & c"        → [a, c], [b, c]
+  #   "(a | b) & (c | d)"  → [a,c], [a,d], [b,c], [b,d]
+  #   "+llms & v"          → expands llms inline, then applies & v
+  sets:
+    # LLM + TTS: switching between g/q/m won't evict v
+    # expands to: [g,v], [q,v], [m,v]
+    standard: "(g | q | m) & v"
+
+    # LLM + TTS + reranker
+    # expands to: [g,v,e], [q,v,e]
+    with_rerank: "(g | q) & v & e"
+
+    # LLM + image generation, no TTS
+    # expands to: [g,sd], [q,sd]
+    creative: "(g | q) & sd"
+
+    # 70B model uses all GPUs, can only run alone
+    # expands to: [L]
+    full: "L"
+
 # hooks: a dictionary of event triggers and actions
 # - optional, default: empty dictionary
 # - the only supported hook is on_startup

proxy/config/config.go

@@ -129,6 +129,12 @@ type Config struct {
 	Profiles           map[string][]string    `yaml:"profiles"`
 	Groups             map[string]GroupConfig `yaml:"groups"` /* key is group ID */
 
+	// swap matrix: solver-based alternative to groups
+	Matrix *MatrixConfig `yaml:"matrix"`
+
+	// populated during validation when matrix is configured
+	ExpandedSets []ExpandedSet `yaml:"-"`
+
 	// for key/value replacements in model's cmd, cmdStop, proxy, checkEndPoint
 	Macros MacroList `yaml:"macros"`
 
@@ -438,22 +444,35 @@ func LoadConfigFromReader(r io.Reader) (Config, error) {
 		config.Models[modelId] = modelConfig
 	}
 
-	config = AddDefaultGroupToConfig(config)
+	// groups XOR matrix
+	if config.Matrix != nil && len(config.Groups) > 0 {
+		return Config{}, fmt.Errorf("config cannot use both 'groups' and 'matrix'")
+	}
 
-	// Validate group members
-	memberUsage := make(map[string]string)
-	for groupID, groupConfig := range config.Groups {
-		prevSet := make(map[string]bool)
-		for _, member := range groupConfig.Members {
-			if _, found := prevSet[member]; found {
-				return Config{}, fmt.Errorf("duplicate model member %s found in group: %s", member, groupID)
-			}
-			prevSet[member] = true
+	if config.Matrix != nil {
+		expandedSets, err := ValidateMatrix(*config.Matrix, config.Models)
+		if err != nil {
+			return Config{}, fmt.Errorf("matrix: %w", err)
+		}
+		config.ExpandedSets = expandedSets
+	} else {
+		config = AddDefaultGroupToConfig(config)
 
-			if existingGroup, exists := memberUsage[member]; exists {
-				return Config{}, fmt.Errorf("model member %s is used in multiple groups: %s and %s", member, existingGroup, groupID)
+		// Validate group members
+		memberUsage := make(map[string]string)
+		for groupID, groupConfig := range config.Groups {
+			prevSet := make(map[string]bool)
+			for _, member := range groupConfig.Members {
+				if _, found := prevSet[member]; found {
+					return Config{}, fmt.Errorf("duplicate model member %s found in group: %s", member, groupID)
+				}
+				prevSet[member] = true
+
+				if existingGroup, exists := memberUsage[member]; exists {
+					return Config{}, fmt.Errorf("model member %s is used in multiple groups: %s and %s", member, existingGroup, groupID)
+				}
+				memberUsage[member] = groupID
 			}
-			memberUsage[member] = groupID
 		}
 	}
 

proxy/config/matrix.go

@@ -0,0 +1,222 @@
+package config
+
+import (
+	"fmt"
+	"regexp"
+	"sort"
+
+	"gopkg.in/yaml.v3"
+)
+
+var mapKeyPattern = regexp.MustCompile(`^[a-zA-Z0-9]{1,8}$`)
+
+// MatrixConfig represents the swap matrix configuration block.
+type MatrixConfig struct {
+	Map        map[string]string `yaml:"map"`
+	EvictCosts map[string]int    `yaml:"evict_costs"`
+	Sets       OrderedSets       `yaml:"sets"`
+}
+
+// SetEntry is a single named set with its DSL expression.
+type SetEntry struct {
+	Name string
+	DSL  string
+}
+
+// OrderedSets preserves YAML definition order of sets (used for tie-breaking).
+type OrderedSets []SetEntry
+
+func (os *OrderedSets) UnmarshalYAML(value *yaml.Node) error {
+	if value.Kind != yaml.MappingNode {
+		return fmt.Errorf("sets must be a mapping")
+	}
+
+	entries := make([]SetEntry, 0, len(value.Content)/2)
+	for i := 0; i < len(value.Content); i += 2 {
+		keyNode := value.Content[i]
+		valueNode := value.Content[i+1]
+
+		var name string
+		if err := keyNode.Decode(&name); err != nil {
+			return fmt.Errorf("failed to decode set name: %w", err)
+		}
+
+		var dsl string
+		if err := valueNode.Decode(&dsl); err != nil {
+			return fmt.Errorf("failed to decode DSL for set %q: %w", name, err)
+		}
+
+		entries = append(entries, SetEntry{Name: name, DSL: dsl})
+	}
+
+	*os = entries
+	return nil
+}
+
+// ExpandedSet is one valid combination of concurrent models (real model names).
+type ExpandedSet struct {
+	SetName string
+	DSL     string
+	Models  []string // real model names, sorted
+}
+
+// ValidateMatrix validates the matrix config and returns all expanded sets.
+func ValidateMatrix(matrix MatrixConfig, models map[string]ModelConfig) ([]ExpandedSet, error) {
+	if len(matrix.Sets) == 0 {
+		return nil, fmt.Errorf("matrix must define at least one set")
+	}
+
+	// Validate map entries
+	if matrix.Map != nil {
+		for id, modelName := range matrix.Map {
+			if !mapKeyPattern.MatchString(id) {
+				return nil, fmt.Errorf("map key %q must be alphanumeric and 1-8 characters", id)
+			}
+			if _, exists := models[modelName]; !exists {
+				return nil, fmt.Errorf("map key %q references unknown model %q", id, modelName)
+			}
+		}
+	}
+
+	// Validate evict_costs
+	if matrix.EvictCosts != nil {
+		for key, cost := range matrix.EvictCosts {
+			if cost <= 0 {
+				return nil, fmt.Errorf("evict_cost for %q must be a positive integer, got %d", key, cost)
+			}
+			if _, ok := matrix.Map[key]; !ok {
+				return nil, fmt.Errorf("evict_costs: unknown map ID %q", key)
+			}
+		}
+	}
+
+	// Build dependency graph for +ref topological sort
+	setNames := make(map[string]bool)
+	for _, entry := range matrix.Sets {
+		setNames[entry.Name] = true
+	}
+
+	deps := make(map[string][]string) // setName -> set names it depends on
+	for _, entry := range matrix.Sets {
+		refs, err := extractRefs(entry.DSL)
+		if err != nil {
+			return nil, fmt.Errorf("set %q: %w", entry.Name, err)
+		}
+		for _, ref := range refs {
+			if !setNames[ref] {
+				return nil, fmt.Errorf("set %q references undefined set %q", entry.Name, ref)
+			}
+		}
+		deps[entry.Name] = refs
+	}
+
+	// Topological sort with cycle detection
+	order, err := topologicalSort(matrix.Sets, deps)
+	if err != nil {
+		return nil, err
+	}
+
+	// Expand sets in topological order
+	resolvedRefs := make(map[string][][]string) // set name -> expanded alias-level combos
+	var allExpanded []ExpandedSet
+	totalCombinations := 0
+
+	// Build ordered map for efficient lookup
+	setDSL := make(map[string]string)
+	for _, entry := range matrix.Sets {
+		setDSL[entry.Name] = entry.DSL
+	}
+
+	for _, name := range order {
+		dsl := setDSL[name]
+		combos, err := ParseAndExpandDSL(dsl, resolvedRefs)
+		if err != nil {
+			return nil, fmt.Errorf("set %q: %w", name, err)
+		}
+
+		resolvedRefs[name] = combos
+
+		// Resolve map IDs to real model names
+		for _, combo := range combos {
+			resolved := make([]string, len(combo))
+			for i, ident := range combo {
+				realName, ok := matrix.Map[ident]
+				if !ok {
+					return nil, fmt.Errorf("set %q: unknown map ID %q", name, ident)
+				}
+				resolved[i] = realName
+			}
+			sort.Strings(resolved)
+			allExpanded = append(allExpanded, ExpandedSet{
+				SetName: name,
+				DSL:     dsl,
+				Models:  resolved,
+			})
+		}
+
+		totalCombinations += len(combos)
+		if totalCombinations > maxDSLExpansions {
+			return nil, fmt.Errorf("total expanded combinations (%d) exceed limit of %d", totalCombinations, maxDSLExpansions)
+		}
+	}
+
+	return allExpanded, nil
+}
+
+// topologicalSort returns set names in dependency order.
+// Returns an error if a cycle is detected.
+func topologicalSort(sets OrderedSets, deps map[string][]string) ([]string, error) {
+	// States: 0 = unvisited, 1 = visiting, 2 = visited
+	state := make(map[string]int)
+	var order []string
+
+	var visit func(name string) error
+	visit = func(name string) error {
+		switch state[name] {
+		case 1:
+			return fmt.Errorf("circular reference detected involving set %q", name)
+		case 2:
+			return nil
+		}
+		state[name] = 1
+
+		for _, dep := range deps[name] {
+			if err := visit(dep); err != nil {
+				return err
+			}
+		}
+
+		state[name] = 2
+		order = append(order, name)
+		return nil
+	}
+
+	// Visit in definition order for deterministic output
+	for _, entry := range sets {
+		if state[entry.Name] == 0 {
+			if err := visit(entry.Name); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	return order, nil
+}
+
+// ResolvedEvictCosts returns a map of real model name -> evict cost,
+// resolving map IDs. Models not listed default to 1.
+func (m *MatrixConfig) ResolvedEvictCosts() map[string]int {
+	costs := make(map[string]int)
+	if m.EvictCosts == nil {
+		return costs
+	}
+	for key, cost := range m.EvictCosts {
+		// Resolve map ID if present
+		if realName, ok := m.Map[key]; ok {
+			costs[realName] = cost
+		} else {
+			costs[key] = cost
+		}
+	}
+	return costs
+}

proxy/config/matrix_dsl.go

@@ -0,0 +1,372 @@
+package config
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+	"unicode"
+)
+
+const maxDSLExpansions = 1000
+
+// Token types for the DSL lexer
+type tokenType int
+
+const (
+	tokIdent  tokenType = iota // model alias or name
+	tokAnd                     // &
+	tokOr                      // |
+	tokLParen                  // (
+	tokRParen                  // )
+	tokRef                     // +setName
+	tokEOF
+)
+
+type token struct {
+	typ tokenType
+	val string
+}
+
+// tokenize splits a DSL string into tokens.
+func tokenize(input string) ([]token, error) {
+	var tokens []token
+	i := 0
+	runes := []rune(input)
+
+	for i < len(runes) {
+		ch := runes[i]
+
+		// skip whitespace
+		if unicode.IsSpace(ch) {
+			i++
+			continue
+		}
+
+		switch ch {
+		case '&':
+			tokens = append(tokens, token{tokAnd, "&"})
+			i++
+		case '|':
+			tokens = append(tokens, token{tokOr, "|"})
+			i++
+		case '(':
+			tokens = append(tokens, token{tokLParen, "("})
+			i++
+		case ')':
+			tokens = append(tokens, token{tokRParen, ")"})
+			i++
+		case '+':
+			// +ref: read the identifier that follows
+			i++
+			start := i
+			for i < len(runes) && isIdentChar(runes[i]) {
+				i++
+			}
+			if i == start {
+				return nil, fmt.Errorf("expected set name after '+' at position %d", start)
+			}
+			tokens = append(tokens, token{tokRef, string(runes[start:i])})
+		default:
+			if isIdentChar(ch) {
+				start := i
+				for i < len(runes) && isIdentChar(runes[i]) {
+					i++
+				}
+				tokens = append(tokens, token{tokIdent, string(runes[start:i])})
+			} else {
+				return nil, fmt.Errorf("unexpected character %q at position %d", ch, i)
+			}
+		}
+	}
+
+	tokens = append(tokens, token{tokEOF, ""})
+	return tokens, nil
+}
+
+func isIdentChar(ch rune) bool {
+	return unicode.IsLetter(ch) || unicode.IsDigit(ch) || ch == '_' || ch == '-' || ch == '.'
+}
+
+// AST node types
+type dslNode interface {
+	dslNode()
+}
+
+type andNode struct {
+	children []dslNode
+}
+
+type orNode struct {
+	children []dslNode
+}
+
+type leafNode struct {
+	name string
+}
+
+type refNode struct {
+	setName string
+}
+
+func (andNode) dslNode()  {}
+func (orNode) dslNode()   {}
+func (leafNode) dslNode() {}
+func (refNode) dslNode()  {}
+
+// parser holds state for recursive-descent parsing.
+type parser struct {
+	tokens []token
+	pos    int
+}
+
+func (p *parser) peek() token {
+	if p.pos < len(p.tokens) {
+		return p.tokens[p.pos]
+	}
+	return token{tokEOF, ""}
+}
+
+func (p *parser) next() token {
+	t := p.peek()
+	if t.typ != tokEOF {
+		p.pos++
+	}
+	return t
+}
+
+func (p *parser) expect(typ tokenType) (token, error) {
+	t := p.next()
+	if t.typ != typ {
+		return t, fmt.Errorf("expected token type %d, got %q", typ, t.val)
+	}
+	return t, nil
+}
+
+// Grammar:
+//
+//	expr    = andExpr
+//	andExpr = orExpr ('&' orExpr)*
+//	orExpr  = atom ('|' atom)*
+//	atom    = ident | '+' ident | '(' expr ')'
+//
+// & binds tighter than |, so "a | b & c" means "a | (b & c)"
+func parse(tokens []token) (dslNode, error) {
+	p := &parser{tokens: tokens}
+	node, err := p.parseExpr()
+	if err != nil {
+		return nil, err
+	}
+	if p.peek().typ != tokEOF {
+		return nil, fmt.Errorf("unexpected token %q after expression", p.peek().val)
+	}
+	return node, nil
+}
+
+func (p *parser) parseExpr() (dslNode, error) {
+	return p.parseOrExpr()
+}
+
+func (p *parser) parseOrExpr() (dslNode, error) {
+	left, err := p.parseAndExpr()
+	if err != nil {
+		return nil, err
+	}
+
+	if p.peek().typ == tokOr {
+		children := []dslNode{left}
+		for p.peek().typ == tokOr {
+			p.next() // consume |
+			right, err := p.parseAndExpr()
+			if err != nil {
+				return nil, err
+			}
+			children = append(children, right)
+		}
+		return orNode{children: children}, nil
+	}
+
+	return left, nil
+}
+
+func (p *parser) parseAndExpr() (dslNode, error) {
+	left, err := p.parseAtom()
+	if err != nil {
+		return nil, err
+	}
+
+	if p.peek().typ == tokAnd {
+		children := []dslNode{left}
+		for p.peek().typ == tokAnd {
+			p.next() // consume &
+			right, err := p.parseAtom()
+			if err != nil {
+				return nil, err
+			}
+			children = append(children, right)
+		}
+		return andNode{children: children}, nil
+	}
+
+	return left, nil
+}
+
+func (p *parser) parseAtom() (dslNode, error) {
+	t := p.peek()
+
+	switch t.typ {
+	case tokIdent:
+		p.next()
+		return leafNode{name: t.val}, nil
+
+	case tokRef:
+		p.next()
+		return refNode{setName: t.val}, nil
+
+	case tokLParen:
+		p.next() // consume (
+		node, err := p.parseExpr()
+		if err != nil {
+			return nil, err
+		}
+		if _, err := p.expect(tokRParen); err != nil {
+			return nil, fmt.Errorf("missing closing parenthesis")
+		}
+		return node, nil
+
+	default:
+		return nil, fmt.Errorf("unexpected token %q", t.val)
+	}
+}
+
+// expand walks the AST and produces all combinations.
+// resolvedRefs contains previously expanded sets for +ref resolution.
+func expand(node dslNode, resolvedRefs map[string][][]string) ([][]string, error) {
+	switch n := node.(type) {
+	case leafNode:
+		return [][]string{{n.name}}, nil
+
+	case refNode:
+		expanded, ok := resolvedRefs[n.setName]
+		if !ok {
+			return nil, fmt.Errorf("unknown set reference +%s", n.setName)
+		}
+		// Return a copy
+		result := make([][]string, len(expanded))
+		for i, combo := range expanded {
+			result[i] = make([]string, len(combo))
+			copy(result[i], combo)
+		}
+		return result, nil
+
+	case orNode:
+		// Union of all children's expansions
+		var result [][]string
+		for _, child := range n.children {
+			childResult, err := expand(child, resolvedRefs)
+			if err != nil {
+				return nil, err
+			}
+			result = append(result, childResult...)
+			if len(result) > maxDSLExpansions {
+				return nil, fmt.Errorf("DSL expansion exceeded %d combinations", maxDSLExpansions)
+			}
+		}
+		return result, nil
+
+	case andNode:
+		// Cartesian product across children
+		result := [][]string{{}} // start with one empty combo
+		for _, child := range n.children {
+			childResult, err := expand(child, resolvedRefs)
+			if err != nil {
+				return nil, err
+			}
+			result = cartesianProduct(result, childResult)
+			if len(result) > maxDSLExpansions {
+				return nil, fmt.Errorf("DSL expansion exceeded %d combinations", maxDSLExpansions)
+			}
+		}
+		return result, nil
+
+	default:
+		return nil, fmt.Errorf("unknown node type %T", node)
+	}
+}
+
+// cartesianProduct computes the cartesian product of two sets of combinations.
+func cartesianProduct(left, right [][]string) [][]string {
+	var result [][]string
+	for _, l := range left {
+		for _, r := range right {
+			combo := make([]string, 0, len(l)+len(r))
+			combo = append(combo, l...)
+			combo = append(combo, r...)
+			result = append(result, combo)
+		}
+	}
+	return result
+}
+
+// ParseAndExpandDSL tokenizes, parses, and expands a DSL string.
+// resolvedRefs contains previously expanded sets for +ref inlining.
+func ParseAndExpandDSL(dsl string, resolvedRefs map[string][][]string) ([][]string, error) {
+	dsl = strings.TrimSpace(dsl)
+	if dsl == "" {
+		return nil, fmt.Errorf("empty DSL expression")
+	}
+
+	tokens, err := tokenize(dsl)
+	if err != nil {
+		return nil, fmt.Errorf("tokenize: %w", err)
+	}
+
+	tree, err := parse(tokens)
+	if err != nil {
+		return nil, fmt.Errorf("parse: %w", err)
+	}
+
+	result, err := expand(tree, resolvedRefs)
+	if err != nil {
+		return nil, err
+	}
+
+	// Deduplicate models within each combination and sort for consistency
+	for i, combo := range result {
+		result[i] = dedupAndSort(combo)
+	}
+
+	return result, nil
+}
+
+// dedupAndSort removes duplicate entries and sorts alphabetically.
+func dedupAndSort(items []string) []string {
+	seen := make(map[string]bool, len(items))
+	var unique []string
+	for _, item := range items {
+		if !seen[item] {
+			seen[item] = true
+			unique = append(unique, item)
+		}
+	}
+	sort.Strings(unique)
+	return unique
+}
+
+// extractRefs scans a DSL string for +ref tokens without full parsing.
+// Used for building the dependency graph for topological sorting.
+func extractRefs(dsl string) ([]string, error) {
+	tokens, err := tokenize(dsl)
+	if err != nil {
+		return nil, err
+	}
+
+	var refs []string
+	seen := make(map[string]bool)
+	for _, t := range tokens {
+		if t.typ == tokRef && !seen[t.val] {
+			seen[t.val] = true
+			refs = append(refs, t.val)
+		}
+	}
+	return refs, nil
+}

proxy/config/matrix_dsl_test.go

@@ -0,0 +1,300 @@
+package config
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDSL_Tokenize(t *testing.T) {
+	tests := []struct {
+		name   string
+		input  string
+		expect []token
+		errMsg string
+	}{
+		{
+			name:  "single identifier",
+			input: "abc",
+			expect: []token{
+				{tokIdent, "abc"},
+				{tokEOF, ""},
+			},
+		},
+		{
+			name:  "identifier with hyphens and dots",
+			input: "model-name.v2",
+			expect: []token{
+				{tokIdent, "model-name.v2"},
+				{tokEOF, ""},
+			},
+		},
+		{
+			name:  "and expression",
+			input: "a & b",
+			expect: []token{
+				{tokIdent, "a"},
+				{tokAnd, "&"},
+				{tokIdent, "b"},
+				{tokEOF, ""},
+			},
+		},
+		{
+			name:  "or expression",
+			input: "a | b",
+			expect: []token{
+				{tokIdent, "a"},
+				{tokOr, "|"},
+				{tokIdent, "b"},
+				{tokEOF, ""},
+			},
+		},
+		{
+			name:  "parentheses",
+			input: "(a | b) & c",
+			expect: []token{
+				{tokLParen, "("},
+				{tokIdent, "a"},
+				{tokOr, "|"},
+				{tokIdent, "b"},
+				{tokRParen, ")"},
+				{tokAnd, "&"},
+				{tokIdent, "c"},
+				{tokEOF, ""},
+			},
+		},
+		{
+			name:  "ref token",
+			input: "+llms & v",
+			expect: []token{
+				{tokRef, "llms"},
+				{tokAnd, "&"},
+				{tokIdent, "v"},
+				{tokEOF, ""},
+			},
+		},
+		{
+			name:  "no whitespace",
+			input: "(a|b)&c",
+			expect: []token{
+				{tokLParen, "("},
+				{tokIdent, "a"},
+				{tokOr, "|"},
+				{tokIdent, "b"},
+				{tokRParen, ")"},
+				{tokAnd, "&"},
+				{tokIdent, "c"},
+				{tokEOF, ""},
+			},
+		},
+		{
+			name:   "empty ref",
+			input:  "+",
+			errMsg: "expected set name after '+'",
+		},
+		{
+			name:   "invalid character",
+			input:  "a @ b",
+			errMsg: "unexpected character",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tokens, err := tokenize(tt.input)
+			if tt.errMsg != "" {
+				require.Error(t, err)
+				assert.Contains(t, err.Error(), tt.errMsg)
+			} else {
+				require.NoError(t, err)
+				assert.Equal(t, tt.expect, tokens)
+			}
+		})
+	}
+}
+
+func TestDSL_ParseAndExpand(t *testing.T) {
+	tests := []struct {
+		name   string
+		dsl    string
+		refs   map[string][][]string
+		expect [][]string
+		errMsg string
+	}{
+		{
+			name:   "single model",
+			dsl:    "L",
+			expect: [][]string{{"L"}},
+		},
+		{
+			name:   "two models with AND",
+			dsl:    "a & b",
+			expect: [][]string{{"a", "b"}},
+		},
+		{
+			name:   "two models with OR",
+			dsl:    "a | b",
+			expect: [][]string{{"a"}, {"b"}},
+		},
+		{
+			name:   "three models with OR",
+			dsl:    "a | b | c",
+			expect: [][]string{{"a"}, {"b"}, {"c"}},
+		},
+		{
+			name: "cartesian product (a|b) & (c|d)",
+			dsl:  "(a | b) & (c | d)",
+			expect: [][]string{
+				{"a", "c"},
+				{"a", "d"},
+				{"b", "c"},
+				{"b", "d"},
+			},
+		},
+		{
+			name: "three-way AND",
+			dsl:  "a & b & c",
+			expect: [][]string{
+				{"a", "b", "c"},
+			},
+		},
+		{
+			name: "(g | q | m) & v",
+			dsl:  "(g | q | m) & v",
+			expect: [][]string{
+				{"g", "v"},
+				{"q", "v"},
+				{"m", "v"},
+			},
+		},
+		{
+			name: "(g | q) & v & e",
+			dsl:  "(g | q) & v & e",
+			expect: [][]string{
+				{"e", "g", "v"},
+				{"e", "q", "v"},
+			},
+		},
+		{
+			name: "precedence: a | b & c means a | (b & c)",
+			dsl:  "a | b & c",
+			expect: [][]string{
+				{"a"},
+				{"b", "c"},
+			},
+		},
+		{
+			name: "+ref inlining",
+			dsl:  "+llms & v",
+			refs: map[string][][]string{
+				"llms": {{"g"}, {"q"}, {"m"}},
+			},
+			expect: [][]string{
+				{"g", "v"},
+				{"q", "v"},
+				{"m", "v"},
+			},
+		},
+		{
+			name: "+ref chained",
+			dsl:  "+with_tts & e",
+			refs: map[string][][]string{
+				"with_tts": {{"g", "v"}, {"q", "v"}, {"m", "v"}},
+			},
+			expect: [][]string{
+				{"e", "g", "v"},
+				{"e", "q", "v"},
+				{"e", "m", "v"},
+			},
+		},
+		{
+			name: "dedup within combination",
+			dsl:  "a & a",
+			expect: [][]string{
+				{"a"},
+			},
+		},
+		{
+			name:   "empty expression",
+			dsl:    "",
+			errMsg: "empty DSL expression",
+		},
+		{
+			name:   "unmatched open paren",
+			dsl:    "(a | b",
+			errMsg: "missing closing parenthesis",
+		},
+		{
+			name:   "unmatched close paren",
+			dsl:    "a | b)",
+			errMsg: "unexpected token",
+		},
+		{
+			name:   "unknown ref",
+			dsl:    "+unknown",
+			errMsg: "unknown set reference +unknown",
+		},
+		{
+			name:   "empty parens",
+			dsl:    "()",
+			errMsg: "unexpected token",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			refs := tt.refs
+			if refs == nil {
+				refs = map[string][][]string{}
+			}
+			result, err := ParseAndExpandDSL(tt.dsl, refs)
+			if tt.errMsg != "" {
+				require.Error(t, err)
+				assert.Contains(t, err.Error(), tt.errMsg)
+			} else {
+				require.NoError(t, err)
+				assert.Equal(t, tt.expect, result)
+			}
+		})
+	}
+}
+
+func TestDSL_ExpansionCap(t *testing.T) {
+	// Build an expression that would exceed 1000 combinations:
+	// (a1|a2|...|a32) & (b1|b2|...|b32) = 1024 combos
+	var aItems, bItems []string
+	for i := 0; i < 32; i++ {
+		aItems = append(aItems, fmt.Sprintf("a%d", i))
+		bItems = append(bItems, fmt.Sprintf("b%d", i))
+	}
+	dsl := fmt.Sprintf("(%s) & (%s)",
+		join(aItems, " | "),
+		join(bItems, " | "),
+	)
+	_, err := ParseAndExpandDSL(dsl, map[string][][]string{})
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "exceeded")
+}
+
+func TestDSL_ExtractRefs(t *testing.T) {
+	refs, err := extractRefs("+llms & v & +other")
+	require.NoError(t, err)
+	assert.Equal(t, []string{"llms", "other"}, refs)
+
+	refs, err = extractRefs("a & b")
+	require.NoError(t, err)
+	assert.Empty(t, refs)
+}
+
+func join(items []string, sep string) string {
+	result := ""
+	for i, item := range items {
+		if i > 0 {
+			result += sep
+		}
+		result += item
+	}
+	return result
+}

proxy/config/matrix_test.go

@@ -0,0 +1,305 @@
+package config
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func makeModels(names ...string) map[string]ModelConfig {
+	m := make(map[string]ModelConfig)
+	for _, name := range names {
+		m[name] = ModelConfig{Cmd: "echo " + name}
+	}
+	return m
+}
+
+func TestValidateMatrix_Basic(t *testing.T) {
+	models := makeModels("gemma", "qwen", "mistral", "voxtral", "llama70B")
+
+	matrix := MatrixConfig{
+		Map: map[string]string{
+			"g": "gemma",
+			"q": "qwen",
+			"m": "mistral",
+			"v": "voxtral",
+			"L": "llama70B",
+		},
+		EvictCosts: map[string]int{
+			"L": 30,
+			"v": 50,
+		},
+		Sets: OrderedSets{
+			{Name: "standard", DSL: "(g | q | m) & v"},
+			{Name: "full", DSL: "L"},
+		},
+	}
+
+	expanded, err := ValidateMatrix(matrix, models)
+	require.NoError(t, err)
+
+	// standard expands to [gemma,voxtral], [qwen,voxtral], [mistral,voxtral]
+	// full expands to [llama70B]
+	assert.Len(t, expanded, 4)
+
+	assert.Equal(t, "standard", expanded[0].SetName)
+	assert.Equal(t, []string{"gemma", "voxtral"}, expanded[0].Models)
+
+	assert.Equal(t, "standard", expanded[1].SetName)
+	assert.Equal(t, []string{"qwen", "voxtral"}, expanded[1].Models)
+
+	assert.Equal(t, "standard", expanded[2].SetName)
+	assert.Equal(t, []string{"mistral", "voxtral"}, expanded[2].Models)
+
+	assert.Equal(t, "full", expanded[3].SetName)
+	assert.Equal(t, []string{"llama70B"}, expanded[3].Models)
+}
+
+func TestValidateMatrix_WithRef(t *testing.T) {
+	models := makeModels("gemma", "qwen", "mistral", "voxtral", "reranker")
+
+	matrix := MatrixConfig{
+		Map: map[string]string{
+			"g": "gemma",
+			"q": "qwen",
+			"m": "mistral",
+			"v": "voxtral",
+			"e": "reranker",
+		},
+		Sets: OrderedSets{
+			{Name: "llms", DSL: "g | q | m"},
+			{Name: "with_tts", DSL: "+llms & v"},
+			{Name: "mega", DSL: "+with_tts & e"},
+		},
+	}
+
+	expanded, err := ValidateMatrix(matrix, models)
+	require.NoError(t, err)
+
+	// llms: [gemma], [qwen], [mistral]
+	// with_tts: [gemma,voxtral], [qwen,voxtral], [mistral,voxtral]
+	// mega: [gemma,reranker,voxtral], [qwen,reranker,voxtral], [mistral,reranker,voxtral]
+	assert.Len(t, expanded, 9)
+
+	// Check mega entries
+	megaEntries := filterBySetName(expanded, "mega")
+	assert.Len(t, megaEntries, 3)
+	assert.Equal(t, []string{"gemma", "reranker", "voxtral"}, megaEntries[0].Models)
+}
+
+func TestValidateMatrix_MapIDRequired(t *testing.T) {
+	// DSL cannot use real model names directly — must use map IDs
+	models := makeModels("gemma", "voxtral")
+
+	matrix := MatrixConfig{
+		Map: map[string]string{"g": "gemma"},
+		Sets: OrderedSets{
+			{Name: "combo", DSL: "g & voxtral"},
+		},
+	}
+
+	_, err := ValidateMatrix(matrix, models)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "unknown map ID")
+}
+
+func TestValidateMatrix_InvalidAliasKey(t *testing.T) {
+	models := makeModels("gemma")
+
+	tests := []struct {
+		name   string
+		alias  string
+		errMsg string
+	}{
+		{"too long", "abcdefghi", "alphanumeric and 1-8 characters"},
+		{"has underscore", "a_b", "alphanumeric and 1-8 characters"},
+		{"has hyphen", "a-b", "alphanumeric and 1-8 characters"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			matrix := MatrixConfig{
+				Map:  map[string]string{tt.alias: "gemma"},
+				Sets: OrderedSets{{Name: "s", DSL: tt.alias}},
+			}
+			_, err := ValidateMatrix(matrix, models)
+			require.Error(t, err)
+			assert.Contains(t, err.Error(), tt.errMsg)
+		})
+	}
+}
+
+func TestValidateMatrix_AliasReferencesUnknownModel(t *testing.T) {
+	models := makeModels("gemma")
+
+	matrix := MatrixConfig{
+		Map:  map[string]string{"x": "nonexistent"},
+		Sets: OrderedSets{{Name: "s", DSL: "x"}},
+	}
+
+	_, err := ValidateMatrix(matrix, models)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "unknown model")
+}
+
+func TestValidateMatrix_EvictCostInvalid(t *testing.T) {
+	models := makeModels("gemma")
+
+	t.Run("zero cost", func(t *testing.T) {
+		matrix := MatrixConfig{
+			Map:        map[string]string{"g": "gemma"},
+			EvictCosts: map[string]int{"g": 0},
+			Sets:       OrderedSets{{Name: "s", DSL: "g"}},
+		}
+		_, err := ValidateMatrix(matrix, models)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "positive integer")
+	})
+
+	t.Run("negative cost", func(t *testing.T) {
+		matrix := MatrixConfig{
+			Map:        map[string]string{"g": "gemma"},
+			EvictCosts: map[string]int{"g": -1},
+			Sets:       OrderedSets{{Name: "s", DSL: "g"}},
+		}
+		_, err := ValidateMatrix(matrix, models)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "positive integer")
+	})
+
+	t.Run("unknown map ID in evict_costs", func(t *testing.T) {
+		matrix := MatrixConfig{
+			Map:        map[string]string{"g": "gemma"},
+			EvictCosts: map[string]int{"unknown": 5},
+			Sets:       OrderedSets{{Name: "s", DSL: "g"}},
+		}
+		_, err := ValidateMatrix(matrix, models)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "unknown map ID")
+	})
+}
+
+func TestValidateMatrix_CycleDetection(t *testing.T) {
+	models := makeModels("gemma")
+
+	matrix := MatrixConfig{
+		Map: map[string]string{"g": "gemma"},
+		Sets: OrderedSets{
+			{Name: "a", DSL: "+b"},
+			{Name: "b", DSL: "+a"},
+		},
+	}
+
+	_, err := ValidateMatrix(matrix, models)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "circular reference")
+}
+
+func TestValidateMatrix_UndefinedRefTarget(t *testing.T) {
+	models := makeModels("gemma")
+
+	matrix := MatrixConfig{
+		Map: map[string]string{"g": "gemma"},
+		Sets: OrderedSets{
+			{Name: "a", DSL: "+nonexistent"},
+		},
+	}
+
+	_, err := ValidateMatrix(matrix, models)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "references undefined set")
+}
+
+func TestValidateMatrix_NoSets(t *testing.T) {
+	_, err := ValidateMatrix(MatrixConfig{}, makeModels("gemma"))
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "at least one set")
+}
+
+func TestValidateMatrix_UnknownMapIDInDSL(t *testing.T) {
+	models := makeModels("gemma")
+
+	matrix := MatrixConfig{
+		Map: map[string]string{"g": "gemma"},
+		Sets: OrderedSets{
+			{Name: "s", DSL: "g & nonexistent"},
+		},
+	}
+
+	_, err := ValidateMatrix(matrix, models)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "unknown map ID")
+}
+
+func TestValidateMatrix_ResolvedEvictCosts(t *testing.T) {
+	mc := &MatrixConfig{
+		Map: map[string]string{
+			"g": "gemma",
+			"L": "llama70B",
+		},
+		EvictCosts: map[string]int{
+			"L": 30,
+			"g": 5,
+		},
+	}
+
+	costs := mc.ResolvedEvictCosts()
+	assert.Equal(t, 30, costs["llama70B"])
+	assert.Equal(t, 5, costs["gemma"])
+}
+
+func TestValidateMatrix_ConfigXOR(t *testing.T) {
+	// groups and matrix both defined
+	yaml := `
+models:
+  model1:
+    cmd: echo model1
+    proxy: http://localhost:8080
+groups:
+  group1:
+    members:
+      - model1
+matrix:
+  sets:
+    s: "model1"
+`
+	_, err := LoadConfigFromReader(strings.NewReader(yaml))
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "cannot use both")
+}
+
+func TestValidateMatrix_ConfigMatrixOnly(t *testing.T) {
+	yaml := `
+models:
+  gemma:
+    cmd: echo gemma
+    proxy: http://localhost:8080
+  qwen:
+    cmd: echo qwen
+    proxy: http://localhost:8081
+matrix:
+  map:
+    g: gemma
+    q: qwen
+  sets:
+    combo: "g | q"
+`
+	cfg, err := LoadConfigFromReader(strings.NewReader(yaml))
+	require.NoError(t, err)
+	assert.NotNil(t, cfg.Matrix)
+	assert.Len(t, cfg.ExpandedSets, 2)
+	// Groups should be empty when matrix is used
+	assert.Empty(t, cfg.Groups)
+}
+
+func filterBySetName(sets []ExpandedSet, name string) []ExpandedSet {
+	var result []ExpandedSet
+	for _, s := range sets {
+		if s.SetName == name {
+			result = append(result, s)
+		}
+	}
+	return result
+}

proxy/matrix.go

@@ -0,0 +1,274 @@
+package proxy
+
+import (
+	"fmt"
+	"net/http"
+	"slices"
+	"sort"
+	"sync"
+
+	"github.com/mostlygeek/llama-swap/proxy/config"
+)
+
+// MatrixSolver contains pure swap-decision logic with no Process dependencies.
+// It is safe for concurrent reads after construction.
+type MatrixSolver struct {
+	expandedSets []config.ExpandedSet // all valid model combinations
+	evictCosts   map[string]int       // real model name -> eviction cost (default 1)
+	modelToSets  map[string][]int     // model name -> indices into expandedSets
+}
+
+// NewMatrixSolver builds a solver from expanded sets and eviction costs.
+func NewMatrixSolver(expandedSets []config.ExpandedSet, evictCosts map[string]int) *MatrixSolver {
+	modelToSets := make(map[string][]int)
+	for i, es := range expandedSets {
+		for _, model := range es.Models {
+			modelToSets[model] = append(modelToSets[model], i)
+		}
+	}
+
+	return &MatrixSolver{
+		expandedSets: expandedSets,
+		evictCosts:   evictCosts,
+		modelToSets:  modelToSets,
+	}
+}
+
+// SolveResult describes what the solver decided.
+type SolveResult struct {
+	Evict     []string // running models that must be stopped
+	TargetSet []string // the chosen set of models (for informational purposes)
+	SetName   string   // name of the chosen set
+	DSL       string   // original DSL expression for the chosen set
+	TotalCost int      // total eviction cost
+}
+
+// Solve determines which models to evict when a model is requested.
+//
+// Algorithm:
+//  1. If requestedModel is already running, no eviction needed.
+//  2. Find all sets containing requestedModel.
+//  3. If no sets found, the model runs alone; evict all running models.
+//  4. For each candidate set, compute cost = sum of evict_costs for running
+//     models NOT in that set.
+//  5. Pick lowest cost. Ties broken by definition order (index in expandedSets).
+//  6. Return models to evict and the chosen set.
+func (s *MatrixSolver) Solve(requestedModel string, runningModels []string) (SolveResult, error) {
+	// If already running, nothing to do
+	if slices.Contains(runningModels, requestedModel) {
+		return SolveResult{}, nil
+	}
+
+	candidateIndices := s.modelToSets[requestedModel]
+
+	// Model not in any set: runs alone, evict everything
+	if len(candidateIndices) == 0 {
+		evict := make([]string, len(runningModels))
+		copy(evict, runningModels)
+		return SolveResult{
+			Evict:     evict,
+			TargetSet: []string{requestedModel},
+		}, nil
+	}
+
+	// Find the cheapest candidate set
+	bestCost := -1
+	bestIdx := -1
+
+	for _, idx := range candidateIndices {
+		setModels := s.expandedSets[idx].Models
+		cost := 0
+		for _, running := range runningModels {
+			if !slices.Contains(setModels, running) {
+				cost += s.evictCost(running)
+			}
+		}
+
+		if bestCost < 0 || cost < bestCost || (cost == bestCost && idx < bestIdx) {
+			bestCost = cost
+			bestIdx = idx
+		}
+	}
+
+	// Determine which running models to evict
+	chosen := s.expandedSets[bestIdx]
+	var evict []string
+	for _, running := range runningModels {
+		if !slices.Contains(chosen.Models, running) {
+			evict = append(evict, running)
+		}
+	}
+
+	return SolveResult{
+		Evict:     evict,
+		TargetSet: chosen.Models,
+		SetName:   chosen.SetName,
+		DSL:       chosen.DSL,
+		TotalCost: bestCost,
+	}, nil
+}
+
+func (s *MatrixSolver) evictCost(model string) int {
+	if cost, ok := s.evictCosts[model]; ok {
+		return cost
+	}
+	return 1
+}
+
+// Matrix manages processes using solver-based swap logic.
+type Matrix struct {
+	sync.Mutex
+	solver         *MatrixSolver
+	processes      map[string]*Process // all processes keyed by real model name
+	config         config.Config
+	proxyLogger    *LogMonitor
+	upstreamLogger *LogMonitor
+}
+
+// NewMatrix creates a Matrix from config. It creates a Process for every
+// model defined in the config (any model can run alone even if not in a set).
+func NewMatrix(cfg config.Config, proxyLogger, upstreamLogger *LogMonitor) *Matrix {
+	processes := make(map[string]*Process)
+	for modelID, modelConfig := range cfg.Models {
+		processLogger := NewLogMonitorWriter(upstreamLogger)
+		process := NewProcess(modelID, cfg.HealthCheckTimeout, modelConfig, processLogger, proxyLogger)
+		processes[modelID] = process
+	}
+
+	evictCosts := cfg.Matrix.ResolvedEvictCosts()
+
+	return &Matrix{
+		solver:         NewMatrixSolver(cfg.ExpandedSets, evictCosts),
+		processes:      processes,
+		config:         cfg,
+		proxyLogger:    proxyLogger,
+		upstreamLogger: upstreamLogger,
+	}
+}
+
+// ProxyRequest handles the swap logic and proxies the request to the model.
+func (m *Matrix) ProxyRequest(modelID string, w http.ResponseWriter, r *http.Request) error {
+	process, ok := m.processes[modelID]
+	if !ok {
+		return fmt.Errorf("model %s not found in matrix", modelID)
+	}
+
+	m.Lock()
+	running := m.runningModels()
+	result, err := m.solver.Solve(modelID, running)
+	if err != nil {
+		m.Unlock()
+		return fmt.Errorf("matrix solver error: %w", err)
+	}
+
+	// Log solver decision
+	if len(result.Evict) > 0 {
+		m.proxyLogger.Debugf("Matrix: model=%s set=%s dsl=%q evict=%v target=%v cost=%d",
+			modelID, result.SetName, result.DSL, result.Evict, result.TargetSet, result.TotalCost)
+	} else if len(running) == 0 {
+		m.proxyLogger.Debugf("Matrix: model=%s starting (no models running)", modelID)
+	} else {
+		m.proxyLogger.Debugf("Matrix: model=%s already running in set=%s dsl=%q", modelID, result.SetName, result.DSL)
+	}
+
+	// Evict models that need to be stopped
+	if len(result.Evict) > 0 {
+		var wg sync.WaitGroup
+		for _, evictModel := range result.Evict {
+			if p, exists := m.processes[evictModel]; exists {
+				wg.Add(1)
+				go func(p *Process) {
+					defer wg.Done()
+					p.Stop()
+				}(p)
+			}
+		}
+		wg.Wait()
+	}
+	m.Unlock()
+
+	// Proxy the request (Process handles on-demand start)
+	process.ProxyRequest(w, r)
+	return nil
+}
+
+// StopProcesses stops all running processes.
+func (m *Matrix) StopProcesses(strategy StopStrategy) {
+	m.Lock()
+	defer m.Unlock()
+
+	var wg sync.WaitGroup
+	for _, process := range m.processes {
+		wg.Add(1)
+		go func(p *Process) {
+			defer wg.Done()
+			switch strategy {
+			case StopImmediately:
+				p.StopImmediately()
+			default:
+				p.Stop()
+			}
+		}(process)
+	}
+	wg.Wait()
+}
+
+// StopProcess stops a single process by model ID.
+func (m *Matrix) StopProcess(modelID string, strategy StopStrategy) error {
+	process, ok := m.processes[modelID]
+	if !ok {
+		return fmt.Errorf("process not found for %s", modelID)
+	}
+
+	switch strategy {
+	case StopImmediately:
+		process.StopImmediately()
+	default:
+		process.Stop()
+	}
+	return nil
+}
+
+// Shutdown shuts down all processes.
+func (m *Matrix) Shutdown() {
+	var wg sync.WaitGroup
+	for _, process := range m.processes {
+		wg.Add(1)
+		go func(p *Process) {
+			defer wg.Done()
+			p.Shutdown()
+		}(process)
+	}
+	wg.Wait()
+}
+
+// RunningModels returns model names currently in StateReady.
+func (m *Matrix) RunningModels() []string {
+	m.Lock()
+	defer m.Unlock()
+	return m.runningModels()
+}
+
+// runningModels returns running model names (caller must hold lock).
+func (m *Matrix) runningModels() []string {
+	var running []string
+	for id, process := range m.processes {
+		if process.CurrentState() == StateReady {
+			running = append(running, id)
+		}
+	}
+	sort.Strings(running)
+	return running
+}
+
+// GetProcess returns the Process for a model.
+func (m *Matrix) GetProcess(modelID string) (*Process, bool) {
+	p, ok := m.processes[modelID]
+	return p, ok
+}
+
+// HasModel returns true if the model is managed by this matrix.
+func (m *Matrix) HasModel(modelID string) bool {
+	_, ok := m.processes[modelID]
+	return ok
+}

proxy/matrix_test.go

@@ -0,0 +1,226 @@
+package proxy
+
+import (
+	"testing"
+
+	"github.com/mostlygeek/llama-swap/proxy/config"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Helper to build expanded sets for solver tests
+func makeExpandedSets(sets ...struct {
+	name   string
+	models []string
+}) []config.ExpandedSet {
+	var result []config.ExpandedSet
+	for _, s := range sets {
+		result = append(result, config.ExpandedSet{
+			SetName: s.name,
+			Models:  s.models,
+		})
+	}
+	return result
+}
+
+func es(name string, models ...string) struct {
+	name   string
+	models []string
+} {
+	return struct {
+		name   string
+		models []string
+	}{name, models}
+}
+
+func TestMatrixSolver_AlreadyRunning(t *testing.T) {
+	solver := NewMatrixSolver(
+		makeExpandedSets(es("s1", "a", "b")),
+		nil,
+	)
+
+	result, err := solver.Solve("a", []string{"a"})
+	require.NoError(t, err)
+	assert.Empty(t, result.Evict)
+	assert.Nil(t, result.TargetSet)
+}
+
+func TestMatrixSolver_NotInAnySet_RunsAlone(t *testing.T) {
+	solver := NewMatrixSolver(
+		makeExpandedSets(es("s1", "a", "b")),
+		nil,
+	)
+
+	// Model "c" not in any set
+	result, err := solver.Solve("c", []string{"a", "b"})
+	require.NoError(t, err)
+	assert.ElementsMatch(t, []string{"a", "b"}, result.Evict)
+	assert.Equal(t, []string{"c"}, result.TargetSet)
+}
+
+func TestMatrixSolver_NotInAnySet_NothingRunning(t *testing.T) {
+	solver := NewMatrixSolver(
+		makeExpandedSets(es("s1", "a", "b")),
+		nil,
+	)
+
+	result, err := solver.Solve("c", []string{})
+	require.NoError(t, err)
+	assert.Empty(t, result.Evict)
+	assert.Equal(t, []string{"c"}, result.TargetSet)
+}
+
+func TestMatrixSolver_SingleSet_EvictsNonMembers(t *testing.T) {
+	// Set: [a, b]. Request a when b and c are running.
+	solver := NewMatrixSolver(
+		makeExpandedSets(es("s1", "a", "b")),
+		nil,
+	)
+
+	result, err := solver.Solve("a", []string{"b", "c"})
+	require.NoError(t, err)
+	// c is not in the set, so it gets evicted. b is in the set, so it stays.
+	assert.Equal(t, []string{"c"}, result.Evict)
+	assert.Equal(t, []string{"a", "b"}, result.TargetSet)
+}
+
+func TestMatrixSolver_PicksLowestCost(t *testing.T) {
+	// Two sets containing model "a":
+	// s1: [a, v]  — if v is running, cost=0; if L is running, cost=30
+	// s2: [a, L]  — if L is running, cost=0; if v is running, cost=50
+	solver := NewMatrixSolver(
+		makeExpandedSets(
+			es("s1", "a", "v"),
+			es("s2", "a", "L"),
+		),
+		map[string]int{"v": 50, "L": 30},
+	)
+
+	// v is running. Switching to a:
+	// s1 cost: v is in s1, so 0
+	// s2 cost: v is NOT in s2, so 50
+	// => pick s1
+	result, err := solver.Solve("a", []string{"v"})
+	require.NoError(t, err)
+	assert.Empty(t, result.Evict)
+	assert.Equal(t, []string{"a", "v"}, result.TargetSet)
+
+	// L is running. Switching to a:
+	// s1 cost: L is NOT in s1, so 30
+	// s2 cost: L is in s2, so 0
+	// => pick s2
+	result, err = solver.Solve("a", []string{"L"})
+	require.NoError(t, err)
+	assert.Empty(t, result.Evict)
+	assert.Equal(t, []string{"a", "L"}, result.TargetSet)
+}
+
+func TestMatrixSolver_TieBreakingByDefinitionOrder(t *testing.T) {
+	// Two sets with identical cost. Definition order should win.
+	solver := NewMatrixSolver(
+		makeExpandedSets(
+			es("s1", "a", "x"),
+			es("s2", "a", "y"),
+		),
+		nil,
+	)
+
+	// Nothing running, both sets cost 0. s1 is first.
+	result, err := solver.Solve("a", []string{})
+	require.NoError(t, err)
+	assert.Empty(t, result.Evict)
+	assert.Equal(t, []string{"a", "x"}, result.TargetSet)
+}
+
+func TestMatrixSolver_EvictCostPreservesExpensive(t *testing.T) {
+	// Model "v" costs 50 to evict, "m" costs 1 (default).
+	// Sets: [g,v], [g,m]
+	// Running: v, m. Request g.
+	// s1=[g,v]: evict m (cost 1), keep v
+	// s2=[g,m]: evict v (cost 50), keep m
+	// => pick s1
+	solver := NewMatrixSolver(
+		makeExpandedSets(
+			es("s1", "g", "v"),
+			es("s2", "g", "m"),
+		),
+		map[string]int{"v": 50},
+	)
+
+	result, err := solver.Solve("g", []string{"v", "m"})
+	require.NoError(t, err)
+	assert.Equal(t, []string{"m"}, result.Evict)
+	assert.Equal(t, []string{"g", "v"}, result.TargetSet)
+}
+
+func TestMatrixSolver_NothingRunning(t *testing.T) {
+	solver := NewMatrixSolver(
+		makeExpandedSets(
+			es("s1", "g", "v"),
+			es("s2", "q", "v"),
+		),
+		nil,
+	)
+
+	result, err := solver.Solve("g", []string{})
+	require.NoError(t, err)
+	assert.Empty(t, result.Evict)
+	assert.Equal(t, []string{"g", "v"}, result.TargetSet)
+}
+
+func TestMatrixSolver_FullScenario(t *testing.T) {
+	// Simulates the example config:
+	// standard: [g,v], [q,v], [m,v]
+	// with_rerank: [g,v,e], [q,v,e]
+	// creative: [g,sd], [q,sd]
+	// full: [L]
+	solver := NewMatrixSolver(
+		makeExpandedSets(
+			es("standard", "g", "v"),
+			es("standard", "q", "v"),
+			es("standard", "m", "v"),
+			es("with_rerank", "e", "g", "v"),
+			es("with_rerank", "e", "q", "v"),
+			es("creative", "g", "sd"),
+			es("creative", "q", "sd"),
+			es("full", "L"),
+		),
+		map[string]int{"v": 50, "L": 30, "whisper": 10},
+	)
+
+	// Running: g, v. Request q.
+	// standard[q,v]: evict g (cost 1), keep v. Total: 1.
+	// with_rerank[q,v,e]: evict g (cost 1), keep v. Total: 1.
+	// => tie, pick first by definition order = standard[q,v]
+	result, err := solver.Solve("q", []string{"g", "v"})
+	require.NoError(t, err)
+	assert.Equal(t, []string{"g"}, result.Evict)
+	assert.Equal(t, []string{"q", "v"}, result.TargetSet)
+
+	// Running: g, v. Request L.
+	// full[L]: evict g (cost 1) + v (cost 50). Total: 51.
+	// Only one set contains L, so pick it.
+	result, err = solver.Solve("L", []string{"g", "v"})
+	require.NoError(t, err)
+	assert.ElementsMatch(t, []string{"g", "v"}, result.Evict)
+	assert.Equal(t, []string{"L"}, result.TargetSet)
+
+	// Running: g, v. Request sd.
+	// creative[g,sd]: evict v (cost 50). Total: 50.
+	// creative[q,sd]: evict g (cost 1) + v (cost 50). Total: 51.
+	// => pick creative[g,sd]
+	result, err = solver.Solve("sd", []string{"g", "v"})
+	require.NoError(t, err)
+	assert.Equal(t, []string{"v"}, result.Evict)
+	assert.Equal(t, []string{"g", "sd"}, result.TargetSet)
+
+	// Running: q, v, e. Request g.
+	// standard[g,v]: evict q (1) + e (1). Total: 2.
+	// with_rerank[g,v,e]: evict q (1). Total: 1.
+	// creative[g,sd]: evict q (1) + v (50) + e (1). Total: 52.
+	// => pick with_rerank[g,v,e]
+	result, err = solver.Solve("g", []string{"e", "q", "v"})
+	require.NoError(t, err)
+	assert.Equal(t, []string{"q"}, result.Evict)
+	assert.Equal(t, []string{"e", "g", "v"}, result.TargetSet)
+}

proxy/proxymanager.go

@@ -77,6 +77,9 @@ type ProxyManager struct {
 
 	processGroups map[string]*ProcessGroup
 
+	// matrix-based swap (mutually exclusive with processGroups)
+	matrix *Matrix
+
 	inFlightCounter *InflightCounter
 
 	// shutdown signaling
@@ -203,10 +206,14 @@ func New(proxyConfig config.Config) *ProxyManager {
 		peerProxy: peerProxy,
 	}
 
-	// create the process groups
-	for groupID := range proxyConfig.Groups {
-		processGroup := NewProcessGroup(groupID, proxyConfig, proxyLogger, upstreamLogger)
-		pm.processGroups[groupID] = processGroup
+	// create either matrix or process groups (mutually exclusive)
+	if proxyConfig.Matrix != nil {
+		pm.matrix = NewMatrix(proxyConfig, proxyLogger, upstreamLogger)
+	} else {
+		for groupID := range proxyConfig.Groups {
+			processGroup := NewProcessGroup(groupID, proxyConfig, proxyLogger, upstreamLogger)
+			pm.processGroups[groupID] = processGroup
+		}
 	}
 
 	pm.setupGinEngine()
@@ -225,18 +232,29 @@ func New(proxyConfig config.Config) *ProxyManager {
 				}
 
 				proxyLogger.Infof("Preloading model: %s", modelID)
-				processGroup, err := pm.swapProcessGroup(modelID)
 
-				if err != nil {
+				var preloadErr error
+				req, _ := http.NewRequest("GET", "/", nil)
+
+				if pm.matrix != nil {
+					preloadErr = pm.matrix.ProxyRequest(modelID, discardWriter, req)
+				} else {
+					processGroup, err := pm.swapProcessGroup(modelID)
+					if err != nil {
+						preloadErr = err
+					} else {
+						preloadErr = processGroup.ProxyRequest(modelID, discardWriter, req)
+					}
+				}
+
+				if preloadErr != nil {
 					event.Emit(ModelPreloadedEvent{
 						ModelName: modelID,
 						Success:   false,
 					})
-					proxyLogger.Errorf("Failed to preload model %s: %v", modelID, err)
+					proxyLogger.Errorf("Failed to preload model %s: %v", modelID, preloadErr)
 					continue
 				} else {
-					req, _ := http.NewRequest("GET", "/", nil)
-					processGroup.ProxyRequest(modelID, discardWriter, req)
 					event.Emit(ModelPreloadedEvent{
 						ModelName: modelID,
 						Success:   true,
@@ -453,6 +471,11 @@ func (pm *ProxyManager) StopProcesses(strategy StopStrategy) {
 	pm.Lock()
 	defer pm.Unlock()
 
+	if pm.matrix != nil {
+		pm.matrix.StopProcesses(strategy)
+		return
+	}
+
 	// stop Processes in parallel
 	var wg sync.WaitGroup
 	for _, processGroup := range pm.processGroups {
@@ -473,6 +496,12 @@ func (pm *ProxyManager) Shutdown() {
 
 	pm.proxyLogger.Debug("Shutdown() called in proxy manager")
 
+	if pm.matrix != nil {
+		pm.matrix.Shutdown()
+		pm.shutdownCancel()
+		return
+	}
+
 	var wg sync.WaitGroup
 	// Send shutdown signal to all process in groups
 	for _, processGroup := range pm.processGroups {
@@ -639,10 +668,16 @@ func (pm *ProxyManager) proxyToUpstream(c *gin.Context) {
 		return
 	}
 
-	processGroup, err := pm.swapProcessGroup(modelID)
-	if err != nil {
-		pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error swapping process group: %s", err.Error()))
-		return
+	var handler func(string, http.ResponseWriter, *http.Request) error
+	if pm.matrix != nil {
+		handler = pm.matrix.ProxyRequest
+	} else {
+		processGroup, err := pm.swapProcessGroup(modelID)
+		if err != nil {
+			pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error swapping process group: %s", err.Error()))
+			return
+		}
+		handler = processGroup.ProxyRequest
 	}
 
 	// rewrite the path
@@ -651,13 +686,13 @@ func (pm *ProxyManager) proxyToUpstream(c *gin.Context) {
 
 	// attempt to record metrics if it is a POST request
 	if pm.metricsMonitor != nil && c.Request.Method == "POST" {
-		if err := pm.metricsMonitor.wrapHandler(modelID, c.Writer, c.Request, processGroup.ProxyRequest); err != nil {
+		if err := pm.metricsMonitor.wrapHandler(modelID, c.Writer, c.Request, handler); err != nil {
 			pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error proxying metrics wrapped request: %s", err.Error()))
 			pm.proxyLogger.Errorf("Error proxying wrapped upstream request for model %s, path=%s", modelID, originalPath)
 			return
 		}
 	} else {
-		if err := processGroup.ProxyRequest(modelID, c.Writer, c.Request); err != nil {
+		if err := handler(modelID, c.Writer, c.Request); err != nil {
 			pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error proxying request: %s", err.Error()))
 			pm.proxyLogger.Errorf("Error proxying upstream request for model %s, path=%s", modelID, originalPath)
 			return
@@ -683,10 +718,16 @@ func (pm *ProxyManager) proxyInferenceHandler(c *gin.Context) {
 
 	modelID, found := pm.config.RealModelName(requestedModel)
 	if found {
-		processGroup, err := pm.swapProcessGroup(modelID)
-		if err != nil {
-			pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error swapping process group: %s", err.Error()))
-			return
+		var localHandler func(string, http.ResponseWriter, *http.Request) error
+		if pm.matrix != nil {
+			localHandler = pm.matrix.ProxyRequest
+		} else {
+			processGroup, err := pm.swapProcessGroup(modelID)
+			if err != nil {
+				pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error swapping process group: %s", err.Error()))
+				return
+			}
+			localHandler = processGroup.ProxyRequest
 		}
 
 		// issue #69 allow custom model names to be sent to upstream
@@ -737,7 +778,7 @@ func (pm *ProxyManager) proxyInferenceHandler(c *gin.Context) {
 		}
 
 		pm.proxyLogger.Debugf("ProxyManager using local Process for model: %s", requestedModel)
-		nextHandler = processGroup.ProxyRequest
+		nextHandler = localHandler
 	} else if pm.peerProxy != nil && pm.peerProxy.HasPeerModel(requestedModel) {
 		pm.proxyLogger.Debugf("ProxyManager using ProxyPeer for model: %s", requestedModel)
 		modelID = requestedModel
@@ -823,15 +864,19 @@ func (pm *ProxyManager) proxyOAIPostFormHandler(c *gin.Context) {
 
 	modelID, found := pm.config.RealModelName(requestedModel)
 	if found {
-		processGroup, err := pm.swapProcessGroup(modelID)
-		if err != nil {
-			pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error swapping process group: %s", err.Error()))
-			return
+		if pm.matrix != nil {
+			nextHandler = pm.matrix.ProxyRequest
+		} else {
+			processGroup, err := pm.swapProcessGroup(modelID)
+			if err != nil {
+				pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error swapping process group: %s", err.Error()))
+				return
+			}
+			nextHandler = processGroup.ProxyRequest
 		}
 
 		useModelName = pm.config.Models[modelID].UseModelName
 		pm.proxyLogger.Debugf("ProxyManager using local Process for model: %s", requestedModel)
-		nextHandler = processGroup.ProxyRequest
 	} else if pm.peerProxy != nil && pm.peerProxy.HasPeerModel(requestedModel) {
 		pm.proxyLogger.Debugf("ProxyManager using ProxyPeer for model: %s", requestedModel)
 		modelID = requestedModel
@@ -942,14 +987,18 @@ func (pm *ProxyManager) proxyGETModelHandler(c *gin.Context) {
 	var modelID string
 
 	if realModelID, found := pm.config.RealModelName(requestedModel); found {
-		processGroup, err := pm.swapProcessGroup(realModelID)
-		if err != nil {
-			pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error swapping process group: %s", err.Error()))
-			return
-		}
 		modelID = realModelID
+		if pm.matrix != nil {
+			nextHandler = pm.matrix.ProxyRequest
+		} else {
+			processGroup, err := pm.swapProcessGroup(realModelID)
+			if err != nil {
+				pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error swapping process group: %s", err.Error()))
+				return
+			}
+			nextHandler = processGroup.ProxyRequest
+		}
 		pm.proxyLogger.Debugf("ProxyManager using local Process for model: %s", requestedModel)
-		nextHandler = processGroup.ProxyRequest
 	} else if pm.peerProxy != nil && pm.peerProxy.HasPeerModel(requestedModel) {
 		modelID = requestedModel
 		pm.proxyLogger.Debugf("ProxyManager using ProxyPeer for model: %s", requestedModel)
@@ -1048,9 +1097,9 @@ func (pm *ProxyManager) listRunningProcessesHandler(context *gin.Context) {
 	context.Header("Content-Type", "application/json")
 	runningProcesses := make([]gin.H, 0) // Default to an empty response.
 
-	for _, processGroup := range pm.processGroups {
-		for _, process := range processGroup.processes {
-			if process.CurrentState() == StateReady {
+	if pm.matrix != nil {
+		for _, modelID := range pm.matrix.RunningModels() {
+			if process, ok := pm.matrix.GetProcess(modelID); ok {
 				runningProcesses = append(runningProcesses, gin.H{
 					"model":       process.ID,
 					"state":       process.state,
@@ -1062,6 +1111,22 @@ func (pm *ProxyManager) listRunningProcessesHandler(context *gin.Context) {
 				})
 			}
 		}
+	} else {
+		for _, processGroup := range pm.processGroups {
+			for _, process := range processGroup.processes {
+				if process.CurrentState() == StateReady {
+					runningProcesses = append(runningProcesses, gin.H{
+						"model":       process.ID,
+						"state":       process.state,
+						"cmd":         process.config.Cmd,
+						"proxy":       process.config.Proxy,
+						"ttl":         process.config.UnloadAfter,
+						"name":        process.config.Name,
+						"description": process.config.Description,
+					})
+				}
+			}
+		}
 	}
 
 	// Put the results under the `running` key.

proxy/proxymanager_api.go

@@ -55,27 +55,28 @@ func (pm *ProxyManager) getModelStatus() []Model {
 	// Iterate over sorted keys
 	for _, modelID := range modelIDs {
 		// Get process state
-		processGroup := pm.findGroupByModelName(modelID)
 		state := "unknown"
-		if processGroup != nil {
-			process := processGroup.processes[modelID]
-			if process != nil {
-				var stateStr string
-				switch process.CurrentState() {
-				case StateReady:
-					stateStr = "ready"
-				case StateStarting:
-					stateStr = "starting"
-				case StateStopping:
-					stateStr = "stopping"
-				case StateShutdown:
-					stateStr = "shutdown"
-				case StateStopped:
-					stateStr = "stopped"
-				default:
-					stateStr = "unknown"
-				}
-				state = stateStr
+		var process *Process
+		if pm.matrix != nil {
+			process, _ = pm.matrix.GetProcess(modelID)
+		} else {
+			processGroup := pm.findGroupByModelName(modelID)
+			if processGroup != nil {
+				process = processGroup.processes[modelID]
+			}
+		}
+		if process != nil {
+			switch process.CurrentState() {
+			case StateReady:
+				state = "ready"
+			case StateStarting:
+				state = "starting"
+			case StateStopping:
+				state = "stopping"
+			case StateShutdown:
+				state = "shutdown"
+			case StateStopped:
+				state = "stopped"
 			}
 		}
 		models = append(models, Model{
@@ -254,18 +255,23 @@ func (pm *ProxyManager) apiUnloadSingleModelHandler(c *gin.Context) {
 		return
 	}
 
-	processGroup := pm.findGroupByModelName(realModelName)
-	if processGroup == nil {
-		pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("process group not found for model %s", requestedModel))
-		return
+	var stopErr error
+	if pm.matrix != nil {
+		stopErr = pm.matrix.StopProcess(realModelName, StopImmediately)
+	} else {
+		processGroup := pm.findGroupByModelName(realModelName)
+		if processGroup == nil {
+			pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("process group not found for model %s", requestedModel))
+			return
+		}
+		stopErr = processGroup.StopProcess(realModelName, StopImmediately)
 	}
 
-	if err := processGroup.StopProcess(realModelName, StopImmediately); err != nil {
-		pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error stopping process: %s", err.Error()))
+	if stopErr != nil {
+		pm.sendErrorResponse(c, http.StatusInternalServerError, fmt.Sprintf("error stopping process: %s", stopErr.Error()))
 		return
-	} else {
-		c.String(http.StatusOK, "OK")
 	}
+	c.String(http.StatusOK, "OK")
 }
 
 func (pm *ProxyManager) apiGetVersion(c *gin.Context) {