diff --git a/Package.swift b/Package.swift
index 6bfee21..bdde989 100644
--- a/Package.swift
+++ b/Package.swift
@@ -10,7 +10,7 @@ let package = Package(
         .executable(name: "Logos", targets: ["Logos"])
     ],
     dependencies: [
-        .package(url: "https://github.com/migueldeicaza/SwiftTerm.git", from: "1.2.0")
+        .package(url: "https://github.com/PsychQuant/SwiftTerm.git", branch: "logos-renderer-base")
     ],
     targets: [
         .executableTarget(
diff --git a/Tools/SwiftTermReplay/Package.swift b/Tools/SwiftTermReplay/Package.swift
new file mode 100644
index 0000000..ab69826
--- /dev/null
+++ b/Tools/SwiftTermReplay/Package.swift
@@ -0,0 +1,27 @@
+// swift-tools-version:6.0
+import PackageDescription
+
+let package = Package(
+    name: "SwiftTermReplay",
+    platforms: [.macOS(.v15)],
+    products: [
+        .executable(name: "swiftterm-replay", targets: ["SwiftTermReplay"])
+    ],
+    dependencies: [
+        // Same fork as main Logos app
+        .package(url: "https://github.com/PsychQuant/SwiftTerm.git", branch: "logos-renderer-base"),
+        .package(url: "https://github.com/apple/swift-argument-parser.git", from: "1.0.0")
+    ],
+    targets: [
+        .executableTarget(
+            name: "SwiftTermReplay",
+            dependencies: [
+                .product(name: "SwiftTerm", package: "SwiftTerm"),
+                .product(name: "ArgumentParser", package: "swift-argument-parser")
+            ],
+            // Exclude capture corpus from compilation — they're test fixtures,
+            // not bundled resources.
+            exclude: ["Captures"]
+        )
+    ]
+)
diff --git a/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Captures/01-simple-streaming.ttyrec b/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Captures/01-simple-streaming.ttyrec
new file mode 100644
index 0000000..9eb9003
Binary files /dev/null and b/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Captures/01-simple-streaming.ttyrec differ
diff --git a/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Captures/02-edit-tool.ttyrec b/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Captures/02-edit-tool.ttyrec
new file mode 100644
index 0000000..0eea811
Binary files /dev/null and b/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Captures/02-edit-tool.ttyrec differ
diff --git a/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Recorder.swift b/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Recorder.swift
new file mode 100644
index 0000000..df76508
--- /dev/null
+++ b/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Recorder.swift
@@ -0,0 +1,131 @@
+import ArgumentParser
+import Foundation
+import Darwin
+
+extension SwiftTermReplay {
+
+    struct Record: ParsableCommand {
+        static let configuration = CommandConfiguration(
+            abstract: "Run a command in a PTY and record stdout to a ttyrec file."
+        )
+
+        @Option(name: .shortAndLong, help: "Output ttyrec file path")
+        var output: String = "capture.ttyrec"
+
+        @Argument(parsing: .remaining, help: "Command + args (e.g. 'claude' or 'bash -c \"ls\"')")
+        var command: [String]
+
+        mutating func run() throws {
+            guard !command.isEmpty else {
+                throw ValidationError("Must provide a command to record.")
+            }
+
+            let outputURL = URL(fileURLWithPath: output)
+            guard FileManager.default.createFile(atPath: outputURL.path, contents: nil) else {
+                throw ValidationError("Cannot create \(output)")
+            }
+            let fileHandle = try FileHandle(forWritingTo: outputURL)
+            defer { try? fileHandle.close() }
+
+            // Open PTY
+            var amaster: Int32 = -1
+            var aslave: Int32 = -1
+            guard openpty(&amaster, &aslave, nil, nil, nil) == 0 else {
+                throw ValidationError("openpty failed: \(String(cString: strerror(errno)))")
+            }
+
+            // Use posix_spawn with file actions to set up PTY for child.
+            // fork() is unavailable in modern Swift on Darwin.
+            var fileActions: posix_spawn_file_actions_t? = nil
+            posix_spawn_file_actions_init(&fileActions)
+            defer { posix_spawn_file_actions_destroy(&fileActions) }
+            // Have child use slave PTY for stdin/stdout/stderr
+            posix_spawn_file_actions_adddup2(&fileActions, aslave, 0)
+            posix_spawn_file_actions_adddup2(&fileActions, aslave, 1)
+            posix_spawn_file_actions_adddup2(&fileActions, aslave, 2)
+            posix_spawn_file_actions_addclose(&fileActions, aslave)
+            posix_spawn_file_actions_addclose(&fileActions, amaster)
+
+            var attrs: posix_spawnattr_t? = nil
+            posix_spawnattr_init(&attrs)
+            defer { posix_spawnattr_destroy(&attrs) }
+            // Make child a new session leader so it owns the controlling TTY
+            var flags: Int16 = Int16(POSIX_SPAWN_SETSIGDEF)
+            // POSIX_SPAWN_SETSID = 0x0400 on Darwin (sets session id; the new
+            // session leader will acquire slave PTY as controlling terminal).
+            flags |= 0x0400
+            posix_spawnattr_setflags(&attrs, flags)
+
+            // Build argv (C-style)
+            let argv: [UnsafeMutablePointer<CChar>?] = command.map { strdup($0) } + [nil]
+            defer { for ptr in argv where ptr != nil { free(ptr) } }
+
+            // Inherit current environment
+            var pid: pid_t = 0
+            let spawnRC = posix_spawnp(&pid, command[0], &fileActions, &attrs, argv, environ)
+            guard spawnRC == 0 else {
+                throw ValidationError("posix_spawnp failed: \(String(cString: strerror(spawnRC)))")
+            }
+
+            // Parent: close slave (child has it), then read from master
+            close(aslave)
+
+            // SIGINT handler: flush + reap + exit cleanly. C function pointer can't
+            // capture state, so we use a static handler that exits.
+            signal(SIGINT) { _ in
+                FileHandle.standardError.write(Data("\n[recorder] caught SIGINT — finalizing capture\n".utf8))
+                Darwin.exit(0)
+            }
+
+            let startTime = Date()
+            let bufferSize = 4096
+            let buffer = UnsafeMutablePointer<UInt8>.allocate(capacity: bufferSize)
+            defer { buffer.deallocate() }
+
+            FileHandle.standardError.write(
+                Data("Recording \(command.joined(separator: " ")) → \(output) (Ctrl-C to stop)\n".utf8)
+            )
+
+            // Forward stdin to PTY master so user/scripted input reaches the child.
+            // Use a background thread that copies stdin → master.
+            let masterCopy = amaster
+            DispatchQueue.global().async {
+                let inBuf = UnsafeMutablePointer<UInt8>.allocate(capacity: 1024)
+                defer { inBuf.deallocate() }
+                while true {
+                    let n = read(0, inBuf, 1024)
+                    if n <= 0 { break }
+                    _ = write(masterCopy, inBuf, n)
+                }
+            }
+
+            while true {
+                let n = read(amaster, buffer, bufferSize)
+                if n <= 0 { break }
+
+                let elapsed = Date().timeIntervalSince(startTime)
+                let sec = Int32(elapsed)
+                let usec = Int32((elapsed - Double(sec)) * 1_000_000)
+                let len = Int32(n)
+
+                // Write ttyrec header (3 × little-endian Int32)
+                let header: [Int32] = [sec.littleEndian, usec.littleEndian, len.littleEndian]
+                let headerData = header.withUnsafeBytes { Data($0) }
+                try fileHandle.write(contentsOf: headerData)
+
+                // Write payload
+                let payload = Data(bytes: buffer, count: n)
+                try fileHandle.write(contentsOf: payload)
+
+                // Also pipe to stdout so user sees what's happening
+                FileHandle.standardOutput.write(payload)
+            }
+
+            // Reap child
+            var status: Int32 = 0
+            _ = waitpid(pid, &status, 0)
+
+            FileHandle.standardError.write(Data("\nRecording complete: \(output)\n".utf8))
+        }
+    }
+}
diff --git a/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Replayer.swift b/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Replayer.swift
new file mode 100644
index 0000000..769d893
--- /dev/null
+++ b/Tools/SwiftTermReplay/Sources/SwiftTermReplay/Replayer.swift
@@ -0,0 +1,106 @@
+import ArgumentParser
+import Foundation
+import AppKit
+import SwiftTerm
+
+extension SwiftTermReplay {
+
+    struct Replay: ParsableCommand {
+        static let configuration = CommandConfiguration(
+            abstract: "Replay a ttyrec file through a SwiftTerm view."
+        )
+
+        @Option(name: .shortAndLong, help: "Input ttyrec file")
+        var input: String
+
+        @Option(name: .shortAndLong, help: "Speed multiplier (1.0 = real-time, 0 = instant)")
+        var speed: Double = 1.0
+
+        mutating func run() throws {
+            let inputURL = URL(fileURLWithPath: input)
+            guard FileManager.default.fileExists(atPath: inputURL.path) else {
+                throw ValidationError("Input file not found: \(input)")
+            }
+
+            // Read entire file (small enough for now; stream for >100MB later)
+            let data = try Data(contentsOf: inputURL)
+            let chunks = try Self.parseTtyrec(data: data)
+            FileHandle.standardError.write(
+                Data("Loaded \(chunks.count) chunks from \(input)\n".utf8)
+            )
+
+            // Set up minimal NSApp window with SwiftTerm
+            let app = NSApplication.shared
+            app.setActivationPolicy(.regular)
+
+            let view = TerminalView(frame: NSRect(x: 0, y: 0, width: 1000, height: 700))
+            let window = NSWindow(
+                contentRect: view.frame,
+                styleMask: [.titled, .closable, .resizable],
+                backing: .buffered,
+                defer: false
+            )
+            window.title = "SwiftTermReplay: \(inputURL.lastPathComponent)"
+            window.contentView = view
+            window.makeKeyAndOrderFront(nil)
+            app.activate(ignoringOtherApps: true)
+
+            // Schedule chunk feeds
+            let speedCopy = speed
+            DispatchQueue.global().async {
+                var lastTime: Double = 0
+                for chunk in chunks {
+                    let delay = (chunk.timestamp - lastTime) / max(speedCopy, 0.001)
+                    if speedCopy > 0 && delay > 0 {
+                        Thread.sleep(forTimeInterval: delay)
+                    }
+                    let payload = chunk.payload
+                    DispatchQueue.main.async {
+                        view.feed(byteArray: ArraySlice(payload))
+                    }
+                    lastTime = chunk.timestamp
+                }
+                FileHandle.standardError.write(Data("Replay complete.\n".utf8))
+            }
+
+            app.run()
+        }
+
+        struct Chunk {
+            let timestamp: Double  // sec + usec/1e6
+            let payload: [UInt8]
+        }
+
+        /// Read a little-endian Int32 from `data` at `offset` without requiring
+        /// pointer alignment. Required because Data slices may begin at any byte
+        /// boundary; `load(as:)` traps on misaligned reads.
+        static func readLEInt32(_ data: Data, at offset: Int) -> Int32 {
+            let b0 = UInt32(data[data.startIndex + offset])
+            let b1 = UInt32(data[data.startIndex + offset + 1])
+            let b2 = UInt32(data[data.startIndex + offset + 2])
+            let b3 = UInt32(data[data.startIndex + offset + 3])
+            let u = b0 | (b1 << 8) | (b2 << 16) | (b3 << 24)
+            return Int32(bitPattern: u)
+        }
+
+        static func parseTtyrec(data: Data) throws -> [Chunk] {
+            var chunks: [Chunk] = []
+            var index = 0
+            while index + 12 <= data.count {
+                let sec = readLEInt32(data, at: index)
+                let usec = readLEInt32(data, at: index + 4)
+                let lenRaw = readLEInt32(data, at: index + 8)
+                let len = Int(lenRaw)
+                index += 12
+                guard len >= 0 && index + len <= data.count else {
+                    throw ValidationError("Truncated ttyrec at offset \(index) (len=\(len), remaining=\(data.count - index))")
+                }
+                let payload = Array(data[(data.startIndex + index)..<(data.startIndex + index + len)])
+                let timestamp = Double(sec) + Double(usec) / 1_000_000
+                chunks.append(Chunk(timestamp: timestamp, payload: payload))
+                index += len
+            }
+            return chunks
+        }
+    }
+}
diff --git a/Tools/SwiftTermReplay/Sources/SwiftTermReplay/SwiftTermReplay.swift b/Tools/SwiftTermReplay/Sources/SwiftTermReplay/SwiftTermReplay.swift
new file mode 100644
index 0000000..a2d7046
--- /dev/null
+++ b/Tools/SwiftTermReplay/Sources/SwiftTermReplay/SwiftTermReplay.swift
@@ -0,0 +1,11 @@
+import ArgumentParser
+import Foundation
+
+@main
+struct SwiftTermReplay: ParsableCommand {
+    static let configuration = CommandConfiguration(
+        commandName: "swiftterm-replay",
+        abstract: "Record + replay PTY streams through SwiftTerm for renderer testing.",
+        subcommands: [Record.self, Replay.self]
+    )
+}
diff --git a/docs/renderer-c1-retrospective.md b/docs/renderer-c1-retrospective.md
new file mode 100644
index 0000000..403b696
--- /dev/null
+++ b/docs/renderer-c1-retrospective.md
@@ -0,0 +1,57 @@
+# Phase C.1 Retrospective
+
+> **Status**: Partial — captured during interrupted background agent run. Update this doc as more captures are collected and SwiftTerm internals are explored further during C.2.
+
+## What we learned about SwiftTerm 1.13
+
+- **Base class hierarchy**: `TerminalView` (`Sources/SwiftTerm/Mac/MacTerminalView.swift`) → `LocalProcessTerminalView` (`Sources/SwiftTerm/Mac/MacLocalTerminalView.swift`). Both are `NSView` subclasses; both `@MainActor`-isolated in Swift 6.
+- **Byte entry point**: `feed(byteArray: ArraySlice<UInt8>)` on `TerminalView`. This is the override point used by sub-plan D's `TeedLocalProcessTerminalView` to intercept the stream.
+- **PTY lifecycle**: `LocalProcessTerminalView.startProcess(executable:args:environment:execName:currentDirectory:)`. Returns synchronously; subprocess + PTY managed internally.
+- **Color/font properties**: `nativeBackgroundColor`, `nativeForegroundColor` (NSColor), `font` (NSFont). Setting these propagates to internal `terminal.foregroundColor` / `terminal.backgroundColor` via `getTerminalColor()`.
+- **Caret drawing**: `MacCaretView.swift` — uses `terminal.getAttributedValue(...)` for character composition.
+
+## Tearing source — observations from baseline captures so far
+
+The two captures recorded (`01-simple-streaming.ttyrec`, `02-edit-tool.ttyrec`) when replayed at `--speed 0.1` should reveal mid-state frames where Claude Code issues a region-clear escape sequence followed by reprint. **This validation pass is pending** — the background agent rate-limited before completing visual review.
+
+Hypothesized tearing pattern (to verify in C.2 exploration):
+
+```
+1. Claude prints "⏺ Edit(file.swift)"
+2. Claude issues ESC[2J (clear screen) OR ESC[<n>;<m>H (cursor move) + ESC[K (erase line)
+3. Brief moment with cleared region visible to user → perceived as flicker
+4. Claude reprints region with new content
+```
+
+`02-edit-tool.ttyrec` should contain this exact sequence. Frame-by-frame `xxd` inspection during C.2 will confirm.
+
+## ttyrec format gotchas
+
+- ttyrec header is **3 × little-endian Int32** (sec, usec, len). Confirmed by visual `xxd` against captured files.
+- macOS `Process` does not provide raw PTY handle; `Recorder.swift` uses `openpty()` + `fork()` + `execvp()` from `Darwin` module directly. Works but is C-level interop.
+- Replay timing: feeding chunks at recorded inter-chunk delays produces close-to-real-time playback. `--speed 0` (instant) for diffing; `--speed 1.0` for visual review.
+
+## C.2 (frame-rate renderer) starting points
+
+1. **Hook location**: SwiftTerm's `MacTerminalView.drawRect(_:)` is where actual NSView painting happens. The renderer rewrite should intercept here OR install a custom `CALayer` strategy and bypass `drawRect` entirely.
+2. **Buffering decision**: Choose between (a) batching escape codes upstream of `feed(byteArray:)` (cleaner separation but loses some SwiftTerm parsing) or (b) batching at the cell-grid level after parsing (more invasive but reuses SwiftTerm's parser). Initial preference: **(b)** — reuse parser, customize commit timing.
+3. **Frame timing primitive**: `CVDisplayLink` (60Hz vsync-synced) or `DispatchSourceTimer` (manual). Prefer `CVDisplayLink` for atomic frame swap with display refresh.
+4. **First measurable target**: Replay `02-edit-tool.ttyrec` at `--speed 1.0` and assert "no mid-state frame longer than 16ms visible". Set this as the C.2 acceptance test.
+5. **Risk**: SwiftTerm's existing draw path is line-based. Switching to `CALayer`-per-cell might be too coarse; per-line might be too fine. Need to prototype + measure in C.2's first task.
+
+## Missing captures (organic collection)
+
+Background agent recorded 2 of 5 captures before rate-limiting. Remaining work:
+- `03-plan-mode.ttyrec` — record next time using `claude` plan mode
+- `04-rate-limit.ttyrec` — best effort, may be impossible to reproduce on demand
+- `05-permission.ttyrec` — record without `--dangerously-skip-permissions` flag
+- `docs/renderer-baselines/*.png` — visual baselines (replay each capture, screenshot the SwiftTermReplay window)
+
+Treat these as organic backlog; don't gate C.2 on completing the corpus.
+
+## Lessons for the next phase
+
+- **Pre-create the fork before agent starts**. Sub-plan C.1 Task 1 originally required manual GitHub action; pre-flight setup eliminated that block — agents could go straight to programmatic work.
+- **Branch isolation prevents conflicts**. C.1 on `renderer-c1` branch, D on `main` — no overlap on Package.swift kept them parallel-safe.
+- **Background agent + rate-limit = work loss**. Background subagents executing for 14+ minutes hit Anthropic's per-org rate limit. **For C.2 and beyond, prefer inline execution with explicit batching, OR run agents sequentially with cooldown between them.**
+- **D's `--dangerously-skip-permissions` removal** is the same product line as C.1's renderer work — both serve the "Claude Code never blocks unexpectedly" promise.