diff --git a/cmd/gnoma/main.go b/cmd/gnoma/main.go
index 59f6d43..65414a8 100644
--- a/cmd/gnoma/main.go
+++ b/cmd/gnoma/main.go
@@ -79,6 +79,13 @@ func main() {
 		logger.Debug("harvested aliases", "count", aliases.Len())
 	}
 
+	// Harvest system inventory
+	inventory := bash.HarvestInventory(context.Background())
+	logger.Debug("system inventory",
+		"tools", len(inventory.Tools),
+		"runtimes", len(inventory.Runtimes),
+	)
+
 	// Re-register bash tool with aliases
 	reg.Register(bash.New(bash.WithAliases(aliases)))
 
@@ -107,13 +114,19 @@ func main() {
 		Logger:           logger,
 	})
 
+	// Build system prompt with inventory
+	systemPrompt := *system
+	if invStr := inventory.String(); invStr != "" {
+		systemPrompt = systemPrompt + "\n\n" + invStr
+	}
+
 	// Create engine
 	eng, err := engine.New(engine.Config{
 		Provider: prov,
 		Router:   rtr,
 		Tools:    reg,
 		Firewall: fw,
-		System:   *system,
+		System:   systemPrompt,
 		Model:    *model,
 		MaxTurns: *maxTurns,
 		Logger:   logger,
diff --git a/docs/essentials/milestones.md b/docs/essentials/milestones.md
index b01da0b..4303de2 100644
--- a/docs/essentials/milestones.md
+++ b/docs/essentials/milestones.md
@@ -17,13 +17,13 @@ depends_on: [vision]
 | M3 | Security Firewall | Request/response scanning, redaction, incognito | M2 |
 | M4 | Router Foundation | Arm registry, pools, task classifier, heuristic selection | M2 |
 | M5 | TUI | Bubble Tea, 6 permission modes, config screen | M3, M4 |
-| M6 | Context Intelligence | Local tokenizer, full compaction (truncate + summarize) | M5 |
+| M6 | Context Intelligence | Local tokenizer, fixed context prefix, full compaction | M5 |
 | M7 | Elfs | Router-integrated sub-agents, parallel work | M4, M6 |
 | M8 | Extensibility | Hooks, skills, MCP client, MCP tool replaceability, plugins | M7 |
 | M9 | Router Advanced | Bandit core, feedback, ensemble strategies, state persistence | M7 |
 | M10 | Persistence & Serve | SQLite sessions, serve mode, coordinator | M7 |
 | M11 | Task Learning | Pattern recognition, task suggestions, persistent tasks | M9 |
-| M12 | Thinking & Structured Output | Thinking modes, schema validation | M2 |
+| M12 | Thinking, Multimodality & Structured Output | Thinking, multimodal I/O, schema validation | M2 |
 | M13 | Auth | OAuth PKCE, keyring, multi-account | M5 |
 | M14 | Observability | Feature flags, telemetry, cost dashboards | M10 |
 | M15 | Web UI | `gnoma web` CLI flag, browser UI via serve mode | M10 |
@@ -43,6 +43,7 @@ depends_on: [vision]
 - [ ] Tool system: bash (with security checks), fs.read, fs.write, fs.edit, fs.glob, fs.grep
 - [ ] Engine agentic loop (stream → tool → re-query → done)
 - [ ] CLI pipe mode (`echo "list files" | gnoma`)
+- [ ] System package inventory: detect installed tools/packages at startup, include in system prompt so the LLM knows what's available
 
 **Exit criteria:** Pipe a coding question in, get a response that uses tools, answer on stdout.
 
@@ -132,7 +133,8 @@ depends_on: [vision]
 
 - [ ] Local tokenizer for accurate token counting
 - [ ] Token tracker with warning states (OK / Warning / Critical)
-- [ ] TruncateStrategy: drop oldest, preserve system + recent
+- [ ] Fixed context prefix: system prompt + loaded md files (CLAUDE.md, project docs) pinned as immutable prefix. Only conversation history after the prefix gets compacted.
+- [ ] TruncateStrategy: drop oldest, preserve system + fixed prefix + recent
 - [ ] SummarizeStrategy: spawn compaction elf, LLM-powered summary, image stripping, boundary messages
 - [ ] Auto-compaction triggers (threshold-based, reactive on 413, circuit breaker after 3 failures)
 - [ ] Pre/post compact hooks
@@ -223,7 +225,7 @@ depends_on: [vision]
 
 **Exit criteria:** gnoma suggests a persistent task after 3+ repetitions. `/task release v1.2.0` executes a saved workflow.
 
-## M12: Thinking, Structured Output & Notebook
+## M12: Thinking, Structured Output, Notebook & Multimodality
 
 **Deliverables:**
 
@@ -232,6 +234,9 @@ depends_on: [vision]
 - [ ] Structured output with JSON schema validation
 - [ ] Retry logic for schema validation failures
 - [ ] NotebookEdit tool: read/write/edit Jupyter notebook cells (.ipynb)
+- [ ] Multimodal input: image support (Anthropic image blocks, OpenAI content parts, Google inline data)
+- [ ] Multimodal input: audio support (where provider supports it)
+- [ ] Multimodal output: image rendering in TUI (sixel/kitty protocol)
 
 ## M13: Auth
 
diff --git a/internal/tool/bash/inventory.go b/internal/tool/bash/inventory.go
new file mode 100644
index 0000000..50f3a4b
--- /dev/null
+++ b/internal/tool/bash/inventory.go
@@ -0,0 +1,318 @@
+package bash
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+)
+
+const inventoryTimeout = 15 * time.Second
+
+// SystemInventory holds dynamically discovered system information.
+type SystemInventory struct {
+	OS       string
+	Shell    string
+	Tools    []string  // all executables found in PATH
+	Runtimes []Runtime // detected runtimes with versions
+}
+
+// Runtime is a detected language runtime or package manager.
+type Runtime struct {
+	Name    string
+	Version string
+}
+
+// HarvestInventory dynamically discovers installed tools and runtimes.
+// No hardcoded lists — scans $PATH and probes for version info.
+func HarvestInventory(ctx context.Context) *SystemInventory {
+	ctx, cancel := context.WithTimeout(ctx, inventoryTimeout)
+	defer cancel()
+
+	inv := &SystemInventory{
+		OS:    detectOS(ctx),
+		Shell: detectShell(),
+	}
+
+	// Scan all executables in PATH
+	allBinaries := scanPATH()
+	inv.Tools = allBinaries
+
+	// Probe for runtimes: try --version on known runtime name patterns
+	inv.Runtimes = probeRuntimes(ctx, allBinaries)
+
+	return inv
+}
+
+// scanPATH collects all unique executable names from $PATH directories.
+func scanPATH() []string {
+	seen := make(map[string]bool)
+	var names []string
+
+	pathDirs := filepath.SplitList(os.Getenv("PATH"))
+	for _, dir := range pathDirs {
+		entries, err := os.ReadDir(dir)
+		if err != nil {
+			continue
+		}
+		for _, entry := range entries {
+			if entry.IsDir() {
+				continue
+			}
+			name := entry.Name()
+			if seen[name] {
+				continue
+			}
+			// Check it's actually executable
+			info, err := entry.Info()
+			if err != nil {
+				continue
+			}
+			if info.Mode()&0o111 != 0 {
+				seen[name] = true
+				names = append(names, name)
+			}
+		}
+	}
+
+	sort.Strings(names)
+	return names
+}
+
+// runtimeCandidate defines how to detect a runtime from a binary name.
+type runtimeCandidate struct {
+	name    string   // display name
+	binary  string   // executable name to look for
+	args    []string // version flag
+}
+
+// knownRuntimePatterns returns binary names that are likely runtimes.
+// We still need a pattern list to know WHICH binaries to try --version on,
+// but the actual detection is dynamic (only probes what's in PATH).
+var runtimePatterns = []runtimeCandidate{
+	// Systems languages
+	{"go", "go", []string{"version"}},
+	{"rust", "rustc", []string{"--version"}},
+	{"zig", "zig", []string{"version"}},
+	{"nim", "nim", []string{"--version"}},
+	{"crystal", "crystal", []string{"--version"}},
+	{"gcc", "gcc", []string{"--version"}},
+	{"clang", "clang", []string{"--version"}},
+	{"nasm", "nasm", []string{"-v"}},
+	// Scripting
+	{"python3", "python3", []string{"--version"}},
+	{"python2", "python2", []string{"--version"}},
+	{"perl", "perl", []string{"--version"}},
+	{"ruby", "ruby", []string{"--version"}},
+	{"lua", "lua", []string{"-v"}},
+	{"luajit", "luajit", []string{"-v"}},
+	{"guile", "guile", []string{"--version"}},
+	// tcl detection is tricky (needs stdin), skipped
+	{"php", "php", []string{"--version"}},
+	{"r", "R", []string{"--version"}},
+	// JS/TS
+	{"node", "node", []string{"--version"}},
+	{"deno", "deno", []string{"--version"}},
+	{"bun", "bun", []string{"--version"}},
+	// JVM
+	{"java", "java", []string{"-version"}},
+	{"kotlin", "kotlin", []string{"-version"}},
+	{"scala", "scala", []string{"-version"}},
+	{"groovy", "groovy", []string{"--version"}},
+	{"clojure", "clj", []string{"--version"}},
+	// Functional
+	{"haskell", "ghc", []string{"--version"}},
+	{"ocaml", "ocaml", []string{"-version"}},
+	{"elixir", "elixir", []string{"--version"}},
+	{"erlang", "erl", []string{"-eval", "io:format(erlang:system_info(otp_release)),halt()."}},
+	{"racket", "racket", []string{"--version"}},
+	// Other
+	{"dart", "dart", []string{"--version"}},
+	{"julia", "julia", []string{"--version"}},
+	{"swift", "swift", []string{"--version"}},
+	// .NET
+	{"dotnet", "dotnet", []string{"--version"}},
+	{"mono", "mono", []string{"--version"}},
+	// Package managers
+	{"cargo", "cargo", []string{"--version"}},
+	{"npm", "npm", []string{"--version"}},
+	{"yarn", "yarn", []string{"--version"}},
+	{"pnpm", "pnpm", []string{"--version"}},
+	{"pip", "pip3", []string{"--version"}},
+	{"gem", "gem", []string{"--version"}},
+	{"composer", "composer", []string{"--version"}},
+	{"mix", "mix", []string{"--version"}},
+	{"cabal", "cabal", []string{"--version"}},
+	{"stack", "stack", []string{"--version"}},
+	{"opam", "opam", []string{"--version"}},
+	{"maven", "mvn", []string{"--version"}},
+	{"gradle", "gradle", []string{"--version"}},
+}
+
+// probeRuntimes checks which runtime candidates exist in the discovered binaries
+// and gets their version info. Runs probes concurrently for speed.
+func probeRuntimes(ctx context.Context, available []string) []Runtime {
+	availSet := make(map[string]bool, len(available))
+	for _, name := range available {
+		availSet[name] = true
+	}
+
+	var mu sync.Mutex
+	var runtimes []Runtime
+	var wg sync.WaitGroup
+
+	// Semaphore to limit concurrent version probes
+	sem := make(chan struct{}, 10)
+
+	for _, candidate := range runtimePatterns {
+		if !availSet[candidate.binary] {
+			continue
+		}
+
+		wg.Add(1)
+		sem <- struct{}{}
+		go func(c runtimeCandidate) {
+			defer wg.Done()
+			defer func() { <-sem }()
+
+			version := probeVersion(ctx, c.binary, c.args)
+			if version != "" {
+				mu.Lock()
+				runtimes = append(runtimes, Runtime{Name: c.name, Version: version})
+				mu.Unlock()
+			}
+		}(candidate)
+	}
+
+	wg.Wait()
+
+	sort.Slice(runtimes, func(i, j int) bool {
+		return runtimes[i].Name < runtimes[j].Name
+	})
+	return runtimes
+}
+
+// probeVersion runs a binary with version args and extracts the first line.
+func probeVersion(ctx context.Context, binary string, args []string) string {
+	ctx, cancel := context.WithTimeout(ctx, 3*time.Second)
+	defer cancel()
+
+	cmd := exec.CommandContext(ctx, binary, args...)
+	cmd.Stdin = nil
+
+	// Some tools print version to stderr (java -version)
+	output, err := cmd.CombinedOutput()
+	if err != nil && len(output) == 0 {
+		return ""
+	}
+
+	// First non-empty line
+	for _, line := range strings.Split(string(output), "\n") {
+		line = strings.TrimSpace(line)
+		if line != "" {
+			return line
+		}
+	}
+	return ""
+}
+
+// String formats the inventory for inclusion in a system prompt.
+func (inv *SystemInventory) String() string {
+	if inv == nil {
+		return ""
+	}
+
+	var b strings.Builder
+	b.WriteString("System environment:\n")
+
+	if inv.OS != "" {
+		fmt.Fprintf(&b, "- OS: %s\n", inv.OS)
+	}
+	if inv.Shell != "" {
+		fmt.Fprintf(&b, "- Shell: %s\n", inv.Shell)
+	}
+	if len(inv.Runtimes) > 0 {
+		b.WriteString("- Runtimes & package managers:\n")
+		for _, rt := range inv.Runtimes {
+			fmt.Fprintf(&b, "  - %s: %s\n", rt.Name, rt.Version)
+		}
+	}
+	if len(inv.Tools) > 0 {
+		fmt.Fprintf(&b, "- Available commands: %d executables in PATH", len(inv.Tools))
+		// Include notable tools only (not the full list — saves tokens)
+		notable := filterNotable(inv.Tools)
+		if len(notable) > 0 {
+			fmt.Fprintf(&b, " (notable: %s)", strings.Join(notable, ", "))
+		}
+		b.WriteString("\n")
+	}
+
+	return b.String()
+}
+
+// notableTools are development-relevant tools worth highlighting in the system prompt.
+var notableTools = map[string]bool{
+	// VCS
+	"git": true, "gh": true, "tea": true, "lazygit": true,
+	// Build
+	"make": true, "cmake": true, "just": true,
+	// Containers
+	"docker": true, "podman": true, "kubectl": true, "helm": true,
+	// Data
+	"jq": true, "yq": true, "rg": true, "fd": true, "fzf": true,
+	// Modern CLI
+	"bat": true, "eza": true, "delta": true, "sd": true, "dust": true,
+	"hyperfine": true, "tokei": true, "scc": true,
+	// Debug
+	"gdb": true, "strace": true, "perf": true, "valgrind": true,
+	// Database
+	"sqlite3": true, "psql": true, "mysql": true, "mongosh": true, "redis-cli": true,
+	// Media
+	"ffmpeg": true, "convert": true,
+	// Infra
+	"terraform": true, "ansible": true,
+	// Network
+	"curl": true, "wget": true, "ssh": true,
+	// Editors
+	"nvim": true, "vim": true,
+	// Multiplexer
+	"tmux": true,
+}
+
+func filterNotable(tools []string) []string {
+	var out []string
+	for _, t := range tools {
+		if notableTools[t] {
+			out = append(out, t)
+		}
+	}
+	return out
+}
+
+func detectOS(ctx context.Context) string {
+	if output := runQuiet(ctx, "uname", "-srm"); output != "" {
+		return strings.TrimSpace(output)
+	}
+	return ""
+}
+
+func detectShell() string {
+	if s := os.Getenv("SHELL"); s != "" {
+		return s
+	}
+	return ""
+}
+
+func runQuiet(ctx context.Context, name string, args ...string) string {
+	cmd := exec.CommandContext(ctx, name, args...)
+	output, err := cmd.Output()
+	if err != nil {
+		return ""
+	}
+	return strings.TrimSpace(string(output))
+}
diff --git a/internal/tool/bash/inventory_test.go b/internal/tool/bash/inventory_test.go
new file mode 100644
index 0000000..761202c
--- /dev/null
+++ b/internal/tool/bash/inventory_test.go
@@ -0,0 +1,93 @@
+package bash
+
+import (
+	"context"
+	"strings"
+	"testing"
+)
+
+func TestScanPATH(t *testing.T) {
+	binaries := scanPATH()
+	if len(binaries) == 0 {
+		t.Fatal("should find at least some executables in PATH")
+	}
+	t.Logf("Found %d executables in PATH", len(binaries))
+
+	// Basic sanity — ls should be in PATH
+	hasLS := false
+	for _, b := range binaries {
+		if b == "ls" {
+			hasLS = true
+			break
+		}
+	}
+	if !hasLS {
+		t.Error("ls should be in PATH")
+	}
+}
+
+func TestHarvestInventory(t *testing.T) {
+	inv := HarvestInventory(context.Background())
+
+	if inv.OS == "" {
+		t.Error("OS should be detected")
+	}
+	t.Logf("OS: %s", inv.OS)
+
+	if inv.Shell == "" {
+		t.Error("Shell should be detected")
+	}
+	t.Logf("Shell: %s", inv.Shell)
+
+	t.Logf("Tools: %d executables in PATH", len(inv.Tools))
+
+	t.Logf("Runtimes (%d):", len(inv.Runtimes))
+	for _, rt := range inv.Runtimes {
+		t.Logf("  %s: %s", rt.Name, rt.Version)
+	}
+
+	// Should find at least Go (we're running Go tests)
+	hasGo := false
+	for _, rt := range inv.Runtimes {
+		if rt.Name == "go" {
+			hasGo = true
+			break
+		}
+	}
+	if !hasGo {
+		t.Error("should detect Go runtime (we're running Go tests)")
+	}
+}
+
+func TestInventory_String(t *testing.T) {
+	inv := &SystemInventory{
+		OS:    "Linux 6.18 x86_64",
+		Shell: "/usr/bin/zsh",
+		Tools: []string{"git", "make", "docker"},
+		Runtimes: []Runtime{
+			{"go", "go version go1.26.1"},
+			{"python3", "Python 3.14.3"},
+		},
+	}
+
+	s := inv.String()
+	if !strings.Contains(s, "Linux") {
+		t.Error("should contain OS")
+	}
+	if !strings.Contains(s, "git") {
+		t.Error("should contain tools")
+	}
+	if !strings.Contains(s, "go:") {
+		t.Error("should contain runtimes")
+	}
+	if !strings.Contains(s, "3 executables in PATH") {
+		t.Errorf("should show tool count, got: %s", s)
+	}
+}
+
+func TestInventory_NilString(t *testing.T) {
+	var inv *SystemInventory
+	if inv.String() != "" {
+		t.Error("nil inventory should return empty string")
+	}
+}