diff --git a/AGENTS.md b/AGENTS.md
index 375ace7..bac78a1 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -37,59 +37,59 @@ These are not preferences. Breaking one is a defect.
 
 ```
 src/
-	index.ts             Public surface. Named exports only, no default export; assembles `defs`.
-	link-life.ts         LinkLife: whether the link lives, and where a request waits for the next one
-	log.ts               SmppLog, the logger contract, and silentLog — the default
-	message.ts           Encoding detection, splitting, bit counting, SMPP date formatting
-	options.ts           SessionOptions, ReconnectOptions, their checks, and `defaults`: every default and internal cap
-	reconnect-loop.ts    ReconnectLoop: backoff, retry timer, stopped-ness
-	result.ts            Result<T>, and an untyped value as error material: errorFrom(), namedValue(), quoted()
-	session.ts           Session: the socket's life, dispatch, events, and the collaborators in session/
-	sms.ts               The live handle emitted as the 'sms' event (sendResp/sendDlr)
-	unanswered-error.ts  UnansweredError: it went out and no answer came back
-	codec/               Bytes <-> PduObject
-		commands.ts      The 33 commands, their ids and ordered parameter lists
-		constants.ts     consts + constsById, and the version that allows optional parameters
-		encodings.ts     GSM 03.38, LATIN1, UCS2, detection, data_coding resolution
-		field-types.ts   Wire types: int8/int16/int32/string/cstring/buffer/arrays
-		framer.ts        PduFramer: a byte stream cut into complete PDUs
-		pdu.ts           pduToObj / objToPdu / pduReturn — synchronous, result-returning
-		refusal.ts       A PDU the codec would not read, and the answer SMPP names for it
-		retained.ts      A PDU copied off the wire so holding it pins nothing else, and what holding it costs
-		statuses.ts      errors + errorsById (ESME_*)
-		tlvs.ts          TLV definitions, tlvsById, the typed read and input shapes, and reading and writing a TLV stream
-	protocol/            What the fields mean
-		bind.ts          Bind directions: which commands bind, what a direction carries, data_sm's stand-in, checkedBind()
-		concat.ts        How a PDU says it is a segment: its UDH, or the sar_* TLVs
-		message-body.ts  Where an inbound body is: short_message, or the message_payload TLV
-		message-ids.ts   Message ids: the peer's notation, the <base>-<n> a segment gets, which response carries one
-		receipt.ts       Delivery receipts: text and TLV parsing, receipt status codes
-		udh.ts           User data header: its length, the concatenation fields of a long SMS and their reference
-		uuid.ts          uuidv7() — the ids the library generates for messages
-	messages/            Whole messages across segments and time
+	index.ts               Public surface. Named exports only, no default export; assembles `defs`.
+	log.ts                 SmppLog, silentLog — the default, and guardedLog(): a logger that cannot throw
+	message.ts             Message bodies: encodeBody/decodeMessage under a data_coding, splitting, bit counting, smppDate/smppTime
+	options.ts             SessionOptions, ReconnectOptions, their checks, and `defaults`: every default and internal cap
+	result.ts              Result<T>, and an untyped value as error material: errorFrom(), namedValue(), quoted()
+	unanswered-error.ts
+	codec/                 Bytes <-> PduObject
+		commands.ts        The 33 commands, their ids and ordered parameter lists
+		constants.ts       consts + constsById, optionalParamsMinVersion, and esm_class's readers: hasUdh(), messageTypeOf()
+		encodings.ts       GSM 03.38, LATIN1, UCS2, detection, data_coding resolution, message class
+		errors.ts          errors + errorsById (ESME_*)
+		pdu-framer.ts      PduFramer
+		pdu.ts             pduToObj / objToPdu / pduReturn — synchronous, result-returning
+		refusal.ts         A PDU the codec would not read, and the answer SMPP names for it
+		retained-pdu.ts    A PDU copied off the wire so holding it pins nothing else, and what holding it costs
+		tlvs.ts            TLV definitions, tlvsById, the typed read and input shapes, and reading and writing a TLV stream
+		types.ts           Wire types: int8/int16/int32/string/cstring/buffer/arrays
+	protocol/              What the fields mean
+		bind.ts            Bind directions: which commands bind, what a direction carries, data_sm's stand-in, checkedBind()
+		concat.ts          How a PDU says it is a segment: its UDH, or the sar_* TLVs
+		dlr.ts             Delivery receipts: text and TLV parsing, receipt status codes
+		message-body.ts    Where an inbound body is: short_message, or the message_payload TLV
+		message-ids.ts     Message ids: the peer's notation, the <base>-<n> a segment gets, which response carries one
+		udh.ts             User data header: its length, the concatenation fields of a long SMS and their reference
+		uuid.ts            uuidv7() — the ids the library generates for messages
+	messages/              Whole messages across segments and time
+		dlr-merger.ts      DlrMerger: per-segment receipts counted into one MessageDlr
 		expiring-groups.ts ExpiringGroups: the capped, weighed, expiring store DlrMerger, HeldMessages and Reassembler share
-		reassembly.ts    Reassembler: capped, expiring multipart groups
-		receipt-merge.ts DlrMerger: per-segment receipts counted into one MessageDlr
-		submit.ts        submitSms composition and the submitSmParams builder
-	session/             One socket's collaborators
-		held-messages.ts HeldMessages: a message from its `sms` event to its answer, capped and expiring, one MessageHold each
-		keepalive.ts     LinkTimers: the enquire_link heartbeat and the idle timeout
+		reassembly.ts      Reassembler: capped, expiring multipart groups
+		submit.ts          submitSms composition and the submitSmParams builder
+	session/               One socket's life, and reconnecting it
+		held-messages.ts   HeldMessages: a message from its `sms` event to its answer, capped and expiring, one MessageHold each
+		idle-waiters.ts    IdleWaiters: waiting for a count to fall to zero, and what is left of a budget
+		incoming-requests.ts IncomingRequests: every request the peer sends — messages, receipts, links, unknown commands
+		link-life.ts       LinkLife: whether the link lives, and where a request waits for the next one
+		link-timers.ts     LinkTimers: the enquire_link heartbeat and the idle timeout
 		outgoing-requests.ts OutgoingRequests: the window, the pending map and the retry
-		pending-requests.ts  PendingRequests: sequence numbers, correlation, timeout, abort
-		requests-in.ts   IncomingRequests: every request the peer sends: messages, receipts, links, unknown commands
-		send-window.ts   SendWindow: the maxOutstanding semaphore
-		transport.ts     PduTransport: the socket a session reads complete PDUs off
-		waiting.ts       IdleWaiters: waiting for a count to fall to zero, and what is left of a budget
-	client/client.ts     client() -> { err, session }
-	server/server.ts     server() -> { err, server }, server owns the listener + close()
+		pdu-transport.ts   PduTransport: the socket a session reads complete PDUs off
+		pending-requests.ts PendingRequests: sequence numbers, correlation, timeout, abort
+		reconnect-loop.ts  ReconnectLoop: backoff, retry timer, stopped-ness
+		send-window.ts     SendWindow: the maxOutstanding semaphore
+		session.ts         Session: the socket's life, dispatch and events, composing the rest of session/
+		sms.ts             The live handle emitted as the 'sms' event (sendResp/sendDlr)
+	client/client.ts       client() -> { err, session }
+	server/server.ts       server() -> { err, server }, server owns the listener + close()
 ```
 
-Imports point one way: `codec` ← `protocol` ← `messages` ← `session/` ← `client`/`server`, and the
-root files sit beside that order. One edge runs against it: `codec/pdu.ts` reads `message.ts`, which
-reads `protocol/udh.ts`, so moving `message.ts` into `protocol/` needs `pdu.ts` off it first. The
-ways back up are the `Session` handed to `createSms()`, `HeldMessages` and `IncomingRequests`, which
-call back into it, and to `OnRequest` and `onConnected` in `options.ts`, all imported as a type
-only.
+Imports point one way: `codec` ← `protocol` ← `messages` ← `session` ← `client`/`server`. At the
+root, `result.ts`, `log.ts` and `unanswered-error.ts` sit below `codec`, and `message.ts` and
+`options.ts` with `protocol`. One edge runs up: `codec/pdu.ts` imports `encodeBody()` and
+`decodeMessage()` from `message.ts`. The ways back up are the `Session` handed to `createSms()`,
+`HeldMessages` and `IncomingRequests`, which call back into it, and to `OnRequest` and `onConnected`
+in `options.ts`, all imported as a type only.
 
 **Parameter order is wire order.** The key order inside `cmds.*.params` is the order the fields are
 written to and read from the buffer. Never sort those alphabetically — the alphabetical-ordering
diff --git a/docs/decisions.md b/docs/decisions.md
index 3828d92..034d884 100644
--- a/docs/decisions.md
+++ b/docs/decisions.md
@@ -295,7 +295,7 @@ rule and an index of the titles below.
   a delivery receipt (0x04).** Appendix B makes a receipt's `stat` the message's final status, so
   0x04 over `ENROUTE` emits the two disagreeing spellings of finality the reading side above has to
   reconcile, and goal 3 has our own senders write the marker 3.4 defines. `sendDlr()` takes the list
-  from `transientStates` in `protocol/receipt.ts`, the same one the reader uses, so the two cannot drift.
+  from `transientStates` in `protocol/dlr.ts`, the same one the reader uses, so the two cannot drift.
   Rejected: 0x04 for every state, for the sake of a peer that classifies on the marker — the cost
   accepted here is that such a peer stops recognising a transient report as a report at all and hands
   its application receipt text as an inbound message, where under 0x04 it would have read the state
@@ -796,11 +796,10 @@ rule and an index of the titles below.
   dev image has no openssl.
 
 - **`src/` is grouped by layer, and imports point down the layers.** Maintainer's call, 2026-09-30,
-  building [plan 3](comprehension-rewrite/plan-3.md): `codec/`, `protocol/`, `messages/`, `session/`,
-  `client/`, `server/`, with the [map](../AGENTS.md#architecture) naming the direction. Serves goal
-  8's reshapeable internals, which a reader has to find before reshaping: every comprehension panel
-  navigated by AGENTS.md's map rather than the flat tree it described. Rejected: `src/` flat until a
-  module has to move for another reason.
+  with the Locality rewrite; the [map](../AGENTS.md#architecture) names the order and places each
+  root file in a layer. Serves goal 8: internals are reshapeable only once a reader can find them,
+  and every comprehension panel navigated by the map. Rejected: `src/` flat until a module has to
+  move for another reason. Valid while the map is what readers navigate by.
 
 - **`test/` stays flat, and a file there is named for the question it answers rather than for the
   module it covers.** Architecture review, 2026-09-08, at 18 test files: what keeps that count honest
diff --git a/eslint.config.js b/eslint.config.js
index 0b22b9d..5eb123a 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -35,12 +35,12 @@ export default tseslint.config(
 	},
 	{
 		// The spec tables are data: their length tracks the specification, not any complexity.
-		files: ['src/codec/{commands,constants,encodings,field-types,statuses,tlvs}.ts'],
+		files: ['src/codec/{commands,constants,encodings,errors,tlvs,types}.ts'],
 		rules: { 'max-lines': 'off' },
 	},
 	{
 		// ESLint counts every ?. and ?? in dlrFromPdu as a branch; the 19 is 26 lines of flat field resolution.
-		files: ['src/protocol/receipt.ts'],
+		files: ['src/protocol/dlr.ts'],
 		rules: { complexity: ['error', 19] },
 	},
 	{
diff --git a/interop-tests/cloudhopper.test.ts b/interop-tests/cloudhopper.test.ts
index 37c3ac7..a31e8e7 100644
--- a/interop-tests/cloudhopper.test.ts
+++ b/interop-tests/cloudhopper.test.ts
@@ -1,8 +1,8 @@
 import assert from 'node:assert/strict';
 import { readFileSync } from 'node:fs';
 import test, { after, describe } from 'node:test';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
 import type { SmppServer } from '../src/server/server.ts';
 import { server } from '../src/server/server.ts';
 
diff --git a/interop-tests/dumbclient.test.ts b/interop-tests/dumbclient.test.ts
index 2edcce9..ba9b82c 100644
--- a/interop-tests/dumbclient.test.ts
+++ b/interop-tests/dumbclient.test.ts
@@ -1,7 +1,7 @@
 import assert from 'node:assert/strict';
 import test, { after, describe } from 'node:test';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
 import type { LogMethod, SmppLog } from '../src/log.ts';
 import { server } from '../src/server/server.ts';
 
@@ -270,7 +270,7 @@ describe('S6 - idle peer, no enquire_link at all', () => {
 		assert.ok(bound, 'dumb-idle never submitted its one message');
 
 		// idleTimeout is 40s from the last byte the peer sent (its submit_sm), never from our own
-		// writes (session/keepalive.ts resets only on inbound data). This test may start running well
+		// writes (session/link-timers.ts resets only on inbound data). This test may start running well
 		// past that mark on its own (S9 above can take a minute) - statsFor(...).closed is set from
 		// a 'close' listener attached at session-creation time, so a close from before this test
 		// even started is still seen; budget is slack for a session that is still open, not a clock.
diff --git a/interop-tests/jasmin.test.ts b/interop-tests/jasmin.test.ts
index a835572..4ee53a0 100644
--- a/interop-tests/jasmin.test.ts
+++ b/interop-tests/jasmin.test.ts
@@ -1,15 +1,15 @@
 import assert from 'node:assert/strict';
 import http from 'node:http';
 import test, { after, describe } from 'node:test';
-import type { Dlr } from '../src/protocol/receipt.ts';
+import type { Dlr } from '../src/protocol/dlr.ts';
 import type { EncodingName } from '../src/codec/encodings.ts';
 import type { PduObject } from '../src/codec/pdu.ts';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
 import { ConcatReference } from '../src/protocol/udh.ts';
 import { client } from '../src/client/client.ts';
 import { closeAfter } from '../test/teardown.ts';
-import { paramText } from '../src/codec/field-types.ts';
+import { paramText } from '../src/codec/types.ts';
 import { server } from '../src/server/server.ts';
 import { encodeMessage, splitMessage } from '../src/message.ts';
 import { submitSmParams } from '../src/messages/submit.ts';
diff --git a/interop-tests/jsmpp.test.ts b/interop-tests/jsmpp.test.ts
index ed2ba0b..aeefb65 100644
--- a/interop-tests/jsmpp.test.ts
+++ b/interop-tests/jsmpp.test.ts
@@ -1,8 +1,8 @@
 import assert from 'node:assert/strict';
 import net from 'node:net';
 import test, { after, describe } from 'node:test';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
 import { PduRefusedError } from '../src/index.ts';
 import { bareTlvHeader, pduBytes } from '../test/raw-pdus.ts';
 import { server } from '../src/server/server.ts';
diff --git a/interop-tests/kannel.test.ts b/interop-tests/kannel.test.ts
index 4ce96be..f82e065 100644
--- a/interop-tests/kannel.test.ts
+++ b/interop-tests/kannel.test.ts
@@ -2,13 +2,13 @@ import assert from 'node:assert/strict';
 import http from 'node:http';
 import test, { after, describe } from 'node:test';
 import type { MessageState } from '../src/codec/constants.ts';
-import type { Dlr } from '../src/protocol/receipt.ts';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Dlr } from '../src/protocol/dlr.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
 import { ConcatReference } from '../src/protocol/udh.ts';
 import { consts } from '../src/codec/constants.ts';
 import { detect, encodings } from '../src/codec/encodings.ts';
-import { paramText } from '../src/codec/field-types.ts';
+import { paramText } from '../src/codec/types.ts';
 import { server } from '../src/server/server.ts';
 import { splitMessage } from '../src/message.ts';
 import { submitSmParams } from '../src/messages/submit.ts';
diff --git a/interop-tests/php.test.ts b/interop-tests/php.test.ts
index 761f138..0c08623 100644
--- a/interop-tests/php.test.ts
+++ b/interop-tests/php.test.ts
@@ -1,8 +1,8 @@
 import assert from 'node:assert/strict';
 import test, { after, describe } from 'node:test';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
-import { paramText } from '../src/codec/field-types.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
+import { paramText } from '../src/codec/types.ts';
 import { isCommand, server } from '../src/index.ts';
 
 const DRIVER = process.env.PHP_DRIVER ?? 'php:8080';
diff --git a/interop-tests/python.test.ts b/interop-tests/python.test.ts
index 138b897..6ed20ee 100644
--- a/interop-tests/python.test.ts
+++ b/interop-tests/python.test.ts
@@ -1,9 +1,9 @@
 import assert from 'node:assert/strict';
 import test, { after, describe } from 'node:test';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
 import { encodings } from '../src/codec/encodings.ts';
-import { paramText } from '../src/codec/field-types.ts';
+import { paramText } from '../src/codec/types.ts';
 import { isCommand, server } from '../src/index.ts';
 
 const DRIVER = process.env.PYTHON_DRIVER ?? 'python:8080';
diff --git a/interop-tests/smppload.test.ts b/interop-tests/smppload.test.ts
index a8ebe1b..b35add5 100644
--- a/interop-tests/smppload.test.ts
+++ b/interop-tests/smppload.test.ts
@@ -1,6 +1,6 @@
 import assert from 'node:assert/strict';
 import test, { after, describe } from 'node:test';
-import type { Session } from '../src/session.ts';
+import type { Session } from '../src/session/session.ts';
 import { server } from '../src/server/server.ts';
 
 const SMPP_PORT = Number(process.env.SMPP_PORT ?? '2775');
diff --git a/interop-tests/smppsim.test.ts b/interop-tests/smppsim.test.ts
index 141eda3..169ad22 100644
--- a/interop-tests/smppsim.test.ts
+++ b/interop-tests/smppsim.test.ts
@@ -1,15 +1,15 @@
 import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
-import type { Dlr } from '../src/protocol/receipt.ts';
+import type { Dlr } from '../src/protocol/dlr.ts';
 import type { EncodingName } from '../src/codec/encodings.ts';
-import type { MessageDlr } from '../src/messages/receipt-merge.ts';
+import type { MessageDlr } from '../src/messages/dlr-merger.ts';
 import type { PduObject } from '../src/codec/pdu.ts';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
 import { client } from '../src/client/client.ts';
 import { closeAfter } from '../test/teardown.ts';
 import { consts } from '../src/codec/constants.ts';
-import { paramText } from '../src/codec/field-types.ts';
+import { paramText } from '../src/codec/types.ts';
 import { server } from '../src/server/server.ts';
 
 const PEER_HOST = process.env.PEER_HOST ?? 'smppsim';
diff --git a/interop-tests/smscsim.test.ts b/interop-tests/smscsim.test.ts
index 35bbb0f..228bc23 100644
--- a/interop-tests/smscsim.test.ts
+++ b/interop-tests/smscsim.test.ts
@@ -1,8 +1,8 @@
 import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
-import type { Dlr } from '../src/protocol/receipt.ts';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Dlr } from '../src/protocol/dlr.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
 import { client } from '../src/client/client.ts';
 import { closeAfter } from '../test/teardown.ts';
 
diff --git a/src/client/client.ts b/src/client/client.ts
index 4243441..046e3f4 100644
--- a/src/client/client.ts
+++ b/src/client/client.ts
@@ -7,8 +7,8 @@ import type { SmsIdFormat } from '../protocol/message-ids.ts';
 import type { Socket } from 'node:net';
 export type { BindType };
 
-import { ReconnectLoop } from '../reconnect-loop.ts';
-import { Session } from '../session.ts';
+import { ReconnectLoop } from '../session/reconnect-loop.ts';
+import { Session } from '../session/session.ts';
 import { checkSessionOptions, defaults } from '../options.ts';
 import { connect as netConnect } from 'node:net';
 import { connect as tlsConnect } from 'node:tls';
diff --git a/src/codec/commands.ts b/src/codec/commands.ts
index 1be9a60..13ebf82 100644
--- a/src/codec/commands.ts
+++ b/src/codec/commands.ts
@@ -1,5 +1,5 @@
-import type { WireType } from './field-types.ts';
-import { buffer, cstring, dest_address_array, int8, unsuccess_sme_array } from './field-types.ts';
+import type { WireType } from './types.ts';
+import { buffer, cstring, dest_address_array, int8, unsuccess_sme_array } from './types.ts';
 
 type CommandSpec = {
 	id: number;
diff --git a/src/codec/statuses.ts b/src/codec/errors.ts
similarity index 100%
rename from src/codec/statuses.ts
rename to src/codec/errors.ts
diff --git a/src/codec/framer.ts b/src/codec/pdu-framer.ts
similarity index 100%
rename from src/codec/framer.ts
rename to src/codec/pdu-framer.ts
diff --git a/src/codec/pdu.ts b/src/codec/pdu.ts
index b27c7cc..8d97194 100644
--- a/src/codec/pdu.ts
+++ b/src/codec/pdu.ts
@@ -1,6 +1,6 @@
 import type { CommandDefinition, CommandName, PduParams, PduParamsInput } from './commands.ts';
-import type { ErrorName } from './statuses.ts';
-import type { ParamValue } from './field-types.ts';
+import type { ErrorName } from './errors.ts';
+import type { ParamValue } from './types.ts';
 import type { PduHeader } from './refusal.ts';
 import type { Result, VoidResult } from '../result.ts';
 import type { TlvInputs, Tlvs } from './tlvs.ts';
@@ -8,8 +8,8 @@ import { PduRefusedError, framingRefusal } from './refusal.ts';
 import { cmds, commandNameById, respNameFor } from './commands.ts';
 import { hasUdh } from './constants.ts';
 import { decodeMessage, encodeBody } from '../message.ts';
-import { errorNameById, errors, isErrorName } from './statuses.ts';
-import { paramNumber, valueText } from './field-types.ts';
+import { errorNameById, errors, isErrorName } from './errors.ts';
+import { paramNumber, valueText } from './types.ts';
 import { parseTlvs, writeTlvs } from './tlvs.ts';
 
 /** The highest sequence number this library hands out; SMPP 3.4 4.7.1 reserves 0x7fffffff. */
diff --git a/src/codec/refusal.ts b/src/codec/refusal.ts
index 317b69d..233503b 100644
--- a/src/codec/refusal.ts
+++ b/src/codec/refusal.ts
@@ -1,5 +1,5 @@
 import type { CommandName } from './commands.ts';
-import type { ErrorName } from './statuses.ts';
+import type { ErrorName } from './errors.ts';
 import { respNameFor } from './commands.ts';
 
 /** A hostile peer must not be able to make us allocate arbitrarily. */
diff --git a/src/codec/retained.ts b/src/codec/retained-pdu.ts
similarity index 94%
rename from src/codec/retained.ts
rename to src/codec/retained-pdu.ts
index 9fda3cc..36c670d 100644
--- a/src/codec/retained.ts
+++ b/src/codec/retained-pdu.ts
@@ -1,6 +1,6 @@
-import type { ParamValue } from './field-types.ts';
+import type { ParamValue } from './types.ts';
 import type { PduObject } from './pdu.ts';
-import { tlvOctets } from './field-types.ts';
+import { tlvOctets } from './types.ts';
 
 /** Wire reads hand back views, so retaining one PDU would pin the whole chunk it arrived in. */
 export function detach(pduObj: PduObject): PduObject {
diff --git a/src/codec/tlvs.ts b/src/codec/tlvs.ts
index d54d57e..fc4d6b0 100644
--- a/src/codec/tlvs.ts
+++ b/src/codec/tlvs.ts
@@ -1,6 +1,6 @@
-import type { ParamValue, TlvValue, WireType } from './field-types.ts';
+import type { ParamValue, TlvValue, WireType } from './types.ts';
 import type { Result } from '../result.ts';
-import { tlv } from './field-types.ts';
+import { tlv } from './types.ts';
 
 /** Only a tag read as octets or as a number may repeat, since its occurrences are listed as one of those. */
 type Definition<Tag> = { id: number; multiple?: false; tag: Tag; type: WireType<Buffer | number | string> }
diff --git a/src/codec/field-types.ts b/src/codec/types.ts
similarity index 100%
rename from src/codec/field-types.ts
rename to src/codec/types.ts
diff --git a/src/index.ts b/src/index.ts
index 80ca7d8..623b60f 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,20 +1,20 @@
 import { cmds, cmdsById } from './codec/commands.ts';
 import { consts, constsById } from './codec/constants.ts';
 import { encodings } from './codec/encodings.ts';
-import { errors, errorsById } from './codec/statuses.ts';
+import { errors, errorsById } from './codec/errors.ts';
 import { tlvs, tlvsById } from './codec/tlvs.ts';
-import { types } from './codec/field-types.ts';
+import { types } from './codec/types.ts';
 
 export { client } from './client/client.ts';
 export { server, SmppServer } from './server/server.ts';
-export { Session } from './session.ts';
+export { Session } from './session/session.ts';
 
 export { cmds, cmdsById, commandNameById, isCommandName } from './codec/commands.ts';
 export { consts, constsById } from './codec/constants.ts';
 export { dataCodingByEncoding, detect, encodingByDataCoding, encodings, isEncodingName, messageClassOf, unencodable } from './codec/encodings.ts';
-export { errorNameById, errors, errorsById, isErrorName } from './codec/statuses.ts';
+export { errorNameById, errors, errorsById, isErrorName } from './codec/errors.ts';
 export { isTlvName, tlvs, tlvsById } from './codec/tlvs.ts';
-export { types } from './codec/field-types.ts';
+export { types } from './codec/types.ts';
 
 export {
 	isCommand,
@@ -36,16 +36,16 @@ export {
 	splitMessage,
 } from './message.ts';
 
-export { dlrFromPdu, parseReceipt, receiptCodes } from './protocol/receipt.ts';
+export { dlrFromPdu, parseReceipt, receiptCodes } from './protocol/dlr.ts';
 export { messageOctets } from './protocol/message-body.ts';
 export { concatOf } from './protocol/concat.ts';
 export { concatInfo } from './protocol/udh.ts';
-export { PduFramer } from './codec/framer.ts';
+export { PduFramer } from './codec/pdu-framer.ts';
 export { uuidv7 } from './protocol/uuid.ts';
 
 export type { BindType, ClientOptions } from './client/client.ts';
-export type { Dlr, Receipt } from './protocol/receipt.ts';
-export type { SendDlrResult, SendRespOptions, Sms } from './sms.ts';
+export type { Dlr, Receipt } from './protocol/dlr.ts';
+export type { SendDlrResult, SendRespOptions, Sms } from './session/sms.ts';
 export type { Concat } from './protocol/concat.ts';
 export type { ConcatInfo } from './protocol/udh.ts';
 export type { Result, VoidResult } from './result.ts';
@@ -66,16 +66,16 @@ export type {
 	SendSmsResult,
 	SessionEvents,
 	SessionOptions,
-} from './session.ts';
+} from './session/session.ts';
 export type { CommandName, PduParams, PduParamsInput } from './codec/commands.ts';
 export type { ConstGroup, MessageState, SubmitMessagingMode } from './codec/constants.ts';
 export type { Encoding, EncodingName, Unencodable } from './codec/encodings.ts';
-export type { ErrorName } from './codec/statuses.ts';
+export type { ErrorName } from './codec/errors.ts';
 export type { PduObject, PduObjectInput, TlvInputs } from './codec/pdu.ts';
 export type { PduHeader } from './codec/refusal.ts';
 export type { SplitOptions } from './message.ts';
 export type { Tlv, TlvDefinition, TlvName, Tlvs } from './codec/tlvs.ts';
-export type { DestAddress, ParamValue, TlvValue, UnsuccessSme, WireType } from './codec/field-types.ts';
+export type { DestAddress, ParamValue, TlvValue, UnsuccessSme, WireType } from './codec/types.ts';
 
 /** The spec tables, grouped the way `larvitsmpp.defs` was in 0.4.0. */
 export const defs = {
diff --git a/src/messages/receipt-merge.ts b/src/messages/dlr-merger.ts
similarity index 99%
rename from src/messages/receipt-merge.ts
rename to src/messages/dlr-merger.ts
index 541ecd7..0b85fe7 100644
--- a/src/messages/receipt-merge.ts
+++ b/src/messages/dlr-merger.ts
@@ -1,4 +1,4 @@
-import type { Dlr } from '../protocol/receipt.ts';
+import type { Dlr } from '../protocol/dlr.ts';
 import type { MessageState } from '../codec/constants.ts';
 import type { SmppLog } from '../log.ts';
 import { ExpiringGroups } from './expiring-groups.ts';
diff --git a/src/messages/reassembly.ts b/src/messages/reassembly.ts
index 97c73ff..f9e13f4 100644
--- a/src/messages/reassembly.ts
+++ b/src/messages/reassembly.ts
@@ -4,9 +4,9 @@ import type { SmppLog } from '../log.ts';
 import { ExpiringGroups } from './expiring-groups.ts';
 import { decodeMessage } from '../message.ts';
 import { defaults } from '../options.ts';
-import { detach, retainedOctets } from '../codec/retained.ts';
+import { detach, retainedOctets } from '../codec/retained-pdu.ts';
 import { messageOctets } from '../protocol/message-body.ts';
-import { paramNumber, paramText } from '../codec/field-types.ts';
+import { paramNumber, paramText } from '../codec/types.ts';
 import { uuidv7 } from '../protocol/uuid.ts';
 
 /** A concatenated message given up on, whose segments the peer has already been answered for. */
diff --git a/src/messages/submit.ts b/src/messages/submit.ts
index 4a65858..4382f13 100644
--- a/src/messages/submit.ts
+++ b/src/messages/submit.ts
@@ -1,5 +1,5 @@
 import type { EncodingName, Unencodable } from '../codec/encodings.ts';
-import type { ParamValue } from '../codec/field-types.ts';
+import type { ParamValue } from '../codec/types.ts';
 import type { SubmitMessagingMode } from '../codec/constants.ts';
 import type { PduObject, PduObjectInput } from '../codec/pdu.ts';
 import type { Result } from '../result.ts';
@@ -7,7 +7,7 @@ import type { SmppLog } from '../log.ts';
 import type { SmsIdNotation } from '../protocol/message-ids.ts';
 import { UnansweredError } from '../unanswered-error.ts';
 import { consts, defaultMessagingMode, isMessagingMode, isSubmitMessagingMode, submitMessagingModes } from '../codec/constants.ts';
-import { cstring, paramText } from '../codec/field-types.ts';
+import { cstring, paramText } from '../codec/types.ts';
 import { dataCodingByEncoding, detect, encodingNames, isEncodingName, unencodable, unencodableText } from '../codec/encodings.ts';
 import { namedValue } from '../result.ts';
 import { normaliseSmsId } from '../protocol/message-ids.ts';
diff --git a/src/options.ts b/src/options.ts
index 79e28a3..f856cf0 100644
--- a/src/options.ts
+++ b/src/options.ts
@@ -1,6 +1,6 @@
 import type { PduObject } from './codec/pdu.ts';
 import type { Result, VoidResult } from './result.ts';
-import type { Session } from './session.ts';
+import type { Session } from './session/session.ts';
 import type { SmppLog } from './log.ts';
 import type { SmsIdFormat } from './protocol/message-ids.ts';
 import type { Socket } from 'node:net';
diff --git a/src/protocol/concat.ts b/src/protocol/concat.ts
index 3aa021d..9932323 100644
--- a/src/protocol/concat.ts
+++ b/src/protocol/concat.ts
@@ -3,7 +3,7 @@ import type { PduObject } from '../codec/pdu.ts';
 import { concatInfo } from './udh.ts';
 import { hasUdh } from '../codec/constants.ts';
 import { messageOctets } from './message-body.ts';
-import { paramNumber } from '../codec/field-types.ts';
+import { paramNumber } from '../codec/types.ts';
 
 /** Where a segment sits in its message, and what ties it to the rest of that message. */
 export type Concat = ConcatInfo & {
diff --git a/src/protocol/receipt.ts b/src/protocol/dlr.ts
similarity index 98%
rename from src/protocol/receipt.ts
rename to src/protocol/dlr.ts
index 7b85584..7782f53 100644
--- a/src/protocol/receipt.ts
+++ b/src/protocol/dlr.ts
@@ -1,12 +1,12 @@
 import type { MessageState } from '../codec/constants.ts';
-import type { TlvValue } from '../codec/field-types.ts';
+import type { TlvValue } from '../codec/types.ts';
 import type { PduObject } from '../codec/pdu.ts';
 import type { SmsIdFormat } from './message-ids.ts';
 import { consts, constsById, hasUdh, messageTypeOf } from '../codec/constants.ts';
 import { encodings } from '../codec/encodings.ts';
 import { messageOctets } from './message-body.ts';
 import { normaliseSmsId } from './message-ids.ts';
-import { paramNumber, paramText } from '../codec/field-types.ts';
+import { paramNumber, paramText } from '../codec/types.ts';
 import { udhLength } from './udh.ts';
 
 /**
diff --git a/src/protocol/message-ids.ts b/src/protocol/message-ids.ts
index 047dea1..b4440d9 100644
--- a/src/protocol/message-ids.ts
+++ b/src/protocol/message-ids.ts
@@ -1,5 +1,5 @@
 import type { CommandName } from '../codec/commands.ts';
-import type { ParamValue } from '../codec/field-types.ts';
+import type { ParamValue } from '../codec/types.ts';
 
 const notations = {
 	decimal: { digits: /^[0-9]+$/, prefix: '' },
diff --git a/src/server/server.ts b/src/server/server.ts
index 2aa4f1f..edca63f 100644
--- a/src/server/server.ts
+++ b/src/server/server.ts
@@ -6,13 +6,13 @@ import type { Server as NetServer, Socket } from 'node:net';
 import type { Server as TlsServer, TlsOptions } from 'node:tls';
 import type { SmppLog } from '../log.ts';
 import { EventEmitter } from 'node:events';
-import { Session } from '../session.ts';
+import { Session } from '../session/session.ts';
 import { bindTypeFromCommand } from '../protocol/bind.ts';
 import { checkSessionOptions, defaults } from '../options.ts';
 import { createServer as createNetServer } from 'node:net';
 import { createServer as createTlsServer } from 'node:tls';
 import { errorFrom } from '../result.ts';
-import { paramText } from '../codec/field-types.ts';
+import { paramText } from '../codec/types.ts';
 import { guardedLog } from '../log.ts';
 import { respNameFor } from '../codec/commands.ts';
 
diff --git a/src/session/held-messages.ts b/src/session/held-messages.ts
index 517472e..eb52310 100644
--- a/src/session/held-messages.ts
+++ b/src/session/held-messages.ts
@@ -1,13 +1,13 @@
-import type { LinkLife } from '../link-life.ts';
+import type { LinkLife } from './link-life.ts';
 import type { PduObject, PduObjectInput } from '../codec/pdu.ts';
 import type { Result } from '../result.ts';
-import type { Session } from '../session.ts';
-import type { SmsHandlers } from '../sms.ts';
+import type { Session } from './session.ts';
+import type { SmsHandlers } from './sms.ts';
 import type { SmppLog } from '../log.ts';
 import { ExpiringGroups } from '../messages/expiring-groups.ts';
-import { IdleWaiters } from './waiting.ts';
-import { createSms } from '../sms.ts';
-import { retainedOctets } from '../codec/retained.ts';
+import { IdleWaiters } from './idle-waiters.ts';
+import { createSms } from './sms.ts';
+import { retainedOctets } from '../codec/retained-pdu.ts';
 
 export type HeldMessagesOptions = {
 	link: LinkLife;
diff --git a/src/session/waiting.ts b/src/session/idle-waiters.ts
similarity index 100%
rename from src/session/waiting.ts
rename to src/session/idle-waiters.ts
diff --git a/src/session/requests-in.ts b/src/session/incoming-requests.ts
similarity index 96%
rename from src/session/requests-in.ts
rename to src/session/incoming-requests.ts
index 73e1b22..153dd01 100644
--- a/src/session/requests-in.ts
+++ b/src/session/incoming-requests.ts
@@ -1,13 +1,13 @@
 import type { Concat } from '../protocol/concat.ts';
-import type { DlrMerger } from '../messages/receipt-merge.ts';
-import type { ErrorName } from '../codec/statuses.ts';
+import type { DlrMerger } from '../messages/dlr-merger.ts';
+import type { ErrorName } from '../codec/errors.ts';
 import type { HeldMessagesOptions } from './held-messages.ts';
-import type { LinkLife } from '../link-life.ts';
+import type { LinkLife } from './link-life.ts';
 import type { LostGroup, Refusal } from '../messages/reassembly.ts';
 import type { OnRequest } from '../options.ts';
 import type { PduObject } from '../codec/pdu.ts';
 import type { VoidResult } from '../result.ts';
-import type { Session } from '../session.ts';
+import type { Session } from './session.ts';
 import type { SmppLog } from '../log.ts';
 import type { SmsIdFormat } from '../protocol/message-ids.ts';
 import { HeldMessages } from './held-messages.ts';
@@ -15,8 +15,8 @@ import { Reassembler } from '../messages/reassembly.ts';
 import { bindCommands, standsInFor } from '../protocol/bind.ts';
 import { defaults } from '../options.ts';
 import { concatOf } from '../protocol/concat.ts';
-import { detach } from '../codec/retained.ts';
-import { dlrFromPdu } from '../protocol/receipt.ts';
+import { detach } from '../codec/retained-pdu.ts';
+import { dlrFromPdu } from '../protocol/dlr.ts';
 import { respIdParams, segmentId } from '../protocol/message-ids.ts';
 import { respNameFor } from '../codec/commands.ts';
 
diff --git a/src/link-life.ts b/src/session/link-life.ts
similarity index 98%
rename from src/link-life.ts
rename to src/session/link-life.ts
index f44f2ea..6b42559 100644
--- a/src/link-life.ts
+++ b/src/session/link-life.ts
@@ -1,5 +1,5 @@
-import type { SmppLog } from './log.ts';
-import type { VoidResult } from './result.ts';
+import type { SmppLog } from '../log.ts';
+import type { VoidResult } from '../result.ts';
 
 export type LinkLifeOptions = {
 	log: SmppLog;
diff --git a/src/session/keepalive.ts b/src/session/link-timers.ts
similarity index 100%
rename from src/session/keepalive.ts
rename to src/session/link-timers.ts
diff --git a/src/session/outgoing-requests.ts b/src/session/outgoing-requests.ts
index 429834e..2dede98 100644
--- a/src/session/outgoing-requests.ts
+++ b/src/session/outgoing-requests.ts
@@ -1,6 +1,6 @@
-import type { LinkLife } from '../link-life.ts';
+import type { LinkLife } from './link-life.ts';
 import type { PduObject, PduObjectInput } from '../codec/pdu.ts';
-import type { PduTransport } from './transport.ts';
+import type { PduTransport } from './pdu-transport.ts';
 import type { Result, VoidResult } from '../result.ts';
 import type { SendOptions } from '../options.ts';
 import type { SmppLog } from '../log.ts';
diff --git a/src/session/transport.ts b/src/session/pdu-transport.ts
similarity index 98%
rename from src/session/transport.ts
rename to src/session/pdu-transport.ts
index e453c0c..df1b5de 100644
--- a/src/session/transport.ts
+++ b/src/session/pdu-transport.ts
@@ -2,7 +2,7 @@ import type { PduObject } from '../codec/pdu.ts';
 import type { SmppLog } from '../log.ts';
 import type { Socket } from 'node:net';
 import type { VoidResult } from '../result.ts';
-import { PduFramer } from '../codec/framer.ts';
+import { PduFramer } from '../codec/pdu-framer.ts';
 import { PduRefusedError } from '../codec/refusal.ts';
 import { pduToObj } from '../codec/pdu.ts';
 
diff --git a/src/reconnect-loop.ts b/src/session/reconnect-loop.ts
similarity index 96%
rename from src/reconnect-loop.ts
rename to src/session/reconnect-loop.ts
index 52a3c92..19dd79a 100644
--- a/src/reconnect-loop.ts
+++ b/src/session/reconnect-loop.ts
@@ -1,7 +1,7 @@
-import type { Result, VoidResult } from './result.ts';
-import type { SmppLog } from './log.ts';
+import type { Result, VoidResult } from '../result.ts';
+import type { SmppLog } from '../log.ts';
 import type { Socket } from 'node:net';
-import { defaults } from './options.ts';
+import { defaults } from '../options.ts';
 
 export type ReconnectLoopOptions = {
 	connect: () => Promise<Result<{ sock: Socket }>>;
diff --git a/src/session/send-window.ts b/src/session/send-window.ts
index 3eabe8f..033a746 100644
--- a/src/session/send-window.ts
+++ b/src/session/send-window.ts
@@ -1,6 +1,6 @@
 import type { SmppLog } from '../log.ts';
 import type { VoidResult } from '../result.ts';
-import { IdleWaiters } from './waiting.ts';
+import { IdleWaiters } from './idle-waiters.ts';
 
 export type SendWindowOptions = {
 	limit: number;
diff --git a/src/session.ts b/src/session/session.ts
similarity index 90%
rename from src/session.ts
rename to src/session/session.ts
index c74e902..326d3dc 100644
--- a/src/session.ts
+++ b/src/session/session.ts
@@ -1,34 +1,34 @@
-import type { Dlr } from './protocol/receipt.ts';
-import type { ErrorName } from './codec/statuses.ts';
-import type { MessageDlr } from './messages/receipt-merge.ts';
-import type { ParamValue } from './codec/field-types.ts';
-import type { PduObject, PduObjectInput, TlvInputs } from './codec/pdu.ts';
-import type { PduRefusedError } from './codec/refusal.ts';
-import type { BindType, LinkEnd, SessionBind } from './protocol/bind.ts';
-import type { CloseOptions, ReconnectOptions, SendOptions, SessionOptions } from './options.ts';
-import type { Result, VoidResult } from './result.ts';
-import type { SendSmsOptions, SendSmsResult } from './messages/submit.ts';
-import type { SmppLog } from './log.ts';
+import type { Dlr } from '../protocol/dlr.ts';
+import type { ErrorName } from '../codec/errors.ts';
+import type { MessageDlr } from '../messages/dlr-merger.ts';
+import type { ParamValue } from '../codec/types.ts';
+import type { PduObject, PduObjectInput, TlvInputs } from '../codec/pdu.ts';
+import type { PduRefusedError } from '../codec/refusal.ts';
+import type { BindType, LinkEnd, SessionBind } from '../protocol/bind.ts';
+import type { CloseOptions, ReconnectOptions, SendOptions, SessionOptions } from '../options.ts';
+import type { Result, VoidResult } from '../result.ts';
+import type { SendSmsOptions, SendSmsResult } from '../messages/submit.ts';
+import type { SmppLog } from '../log.ts';
 import type { Sms } from './sms.ts';
 import type { Socket } from 'node:net';
-import { DlrMerger } from './messages/receipt-merge.ts';
+import { DlrMerger } from '../messages/dlr-merger.ts';
 import { EventEmitter } from 'node:events';
-import { IncomingRequests } from './session/requests-in.ts';
+import { IncomingRequests } from './incoming-requests.ts';
 import { LinkLife } from './link-life.ts';
-import { LinkTimers } from './session/keepalive.ts';
-import { OutgoingRequests } from './session/outgoing-requests.ts';
-import { PduTransport } from './session/transport.ts';
+import { LinkTimers } from './link-timers.ts';
+import { OutgoingRequests } from './outgoing-requests.ts';
+import { PduTransport } from './pdu-transport.ts';
 import { ReconnectLoop } from './reconnect-loop.ts';
-import { leftOf } from './session/waiting.ts';
-import { errorFrom } from './result.ts';
-import { optionalParamsMinVersion } from './codec/constants.ts';
-import { bindCarries, checkedBind } from './protocol/bind.ts';
-import { defaults } from './options.ts';
-import { isResp, objToPdu, pduReturn } from './codec/pdu.ts';
-import { refusalAnswer } from './codec/refusal.ts';
-import { guardedLog } from './log.ts';
-import { submitSms, unsent } from './messages/submit.ts';
-import { ConcatReference } from './protocol/udh.ts';
+import { leftOf } from './idle-waiters.ts';
+import { errorFrom } from '../result.ts';
+import { optionalParamsMinVersion } from '../codec/constants.ts';
+import { bindCarries, checkedBind } from '../protocol/bind.ts';
+import { defaults } from '../options.ts';
+import { isResp, objToPdu, pduReturn } from '../codec/pdu.ts';
+import { refusalAnswer } from '../codec/refusal.ts';
+import { guardedLog } from '../log.ts';
+import { submitSms, unsent } from '../messages/submit.ts';
+import { ConcatReference } from '../protocol/udh.ts';
 
 export type {
 	CloseOptions,
diff --git a/src/sms.ts b/src/session/sms.ts
similarity index 90%
rename from src/sms.ts
rename to src/session/sms.ts
index aadcab6..2270f72 100644
--- a/src/sms.ts
+++ b/src/session/sms.ts
@@ -1,17 +1,17 @@
-import type { ErrorName } from './codec/statuses.ts';
-import type { MessageState } from './codec/constants.ts';
-import type { PduObject, PduObjectInput, TlvInputs } from './codec/pdu.ts';
-import type { Result, VoidResult } from './result.ts';
+import type { ErrorName } from '../codec/errors.ts';
+import type { MessageState } from '../codec/constants.ts';
+import type { PduObject, PduObjectInput, TlvInputs } from '../codec/pdu.ts';
+import type { Result, VoidResult } from '../result.ts';
 import type { Session } from './session.ts';
-import { UnansweredError } from './unanswered-error.ts';
-import { consts } from './codec/constants.ts';
-import { decodeSegments } from './messages/reassembly.ts';
-import { messageClassOf } from './codec/encodings.ts';
-import { paramText } from './codec/field-types.ts';
-import { receiptCodes, transientStates } from './protocol/receipt.ts';
-import { smppDate } from './message.ts';
-import { respIdParams, segmentId } from './protocol/message-ids.ts';
-import { uuidv7 } from './protocol/uuid.ts';
+import { UnansweredError } from '../unanswered-error.ts';
+import { consts } from '../codec/constants.ts';
+import { decodeSegments } from '../messages/reassembly.ts';
+import { messageClassOf } from '../codec/encodings.ts';
+import { paramText } from '../codec/types.ts';
+import { receiptCodes, transientStates } from '../protocol/dlr.ts';
+import { smppDate } from '../message.ts';
+import { respIdParams, segmentId } from '../protocol/message-ids.ts';
+import { uuidv7 } from '../protocol/uuid.ts';
 
 /** `pduObjs` holds what the peer took, so a partial failure names what is already receipted. */
 export type SendDlrResult = {
diff --git a/test/declared-alphabet.test.ts b/test/declared-alphabet.test.ts
index 33bf704..66481aa 100644
--- a/test/declared-alphabet.test.ts
+++ b/test/declared-alphabet.test.ts
@@ -5,10 +5,10 @@ import { client } from '../src/client/client.ts';
 import { closeAfter } from './teardown.ts';
 import { consts } from '../src/codec/constants.ts';
 import { decodeMessage } from '../src/message.ts';
-import { dlrFromPdu } from '../src/protocol/receipt.ts';
+import { dlrFromPdu } from '../src/protocol/dlr.ts';
 import { encodingByDataCoding, encodings } from '../src/codec/encodings.ts';
 import { objToPdu, pduToObj } from '../src/codec/pdu.ts';
-import { paramNumber } from '../src/codec/field-types.ts';
+import { paramNumber } from '../src/codec/types.ts';
 import { server } from '../src/server/server.ts';
 import type { PduObject } from '../src/codec/pdu.ts';
 
diff --git a/test/dlr.test.ts b/test/dlr.test.ts
index 0dfa471..b48540a 100644
--- a/test/dlr.test.ts
+++ b/test/dlr.test.ts
@@ -1,7 +1,7 @@
 import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
 import { consts } from '../src/codec/constants.ts';
-import { dlrFromPdu, parseReceipt, receiptCodes } from '../src/protocol/receipt.ts';
+import { dlrFromPdu, parseReceipt, receiptCodes } from '../src/protocol/dlr.ts';
 import { encodeMessage } from '../src/message.ts';
 import { objToPdu, pduToObj } from '../src/codec/pdu.ts';
 import type { PduObject, TlvInputs } from '../src/codec/pdu.ts';
diff --git a/test/dummy-smsc.ts b/test/dummy-smsc.ts
index 2a12f82..6f6d9af 100644
--- a/test/dummy-smsc.ts
+++ b/test/dummy-smsc.ts
@@ -1,8 +1,8 @@
 import assert from 'node:assert/strict';
 import net from 'node:net';
-import type { Session } from '../src/session.ts';
+import type { Session } from '../src/session/session.ts';
 import type { TestContext } from 'node:test';
-import { PduFramer } from '../src/codec/framer.ts';
+import { PduFramer } from '../src/codec/pdu-framer.ts';
 import { client } from '../src/client/client.ts';
 import { closeAfter, closeListenerAfter } from './teardown.ts';
 import { consts } from '../src/codec/constants.ts';
diff --git a/test/interop.test.ts b/test/interop.test.ts
index d2638f8..7e658c2 100644
--- a/test/interop.test.ts
+++ b/test/interop.test.ts
@@ -2,7 +2,7 @@ import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
 import reference from 'smpp';
 import type { ReferenceSession } from 'smpp';
-import type { Sms } from '../src/sms.ts';
+import type { Sms } from '../src/session/sms.ts';
 import { client } from '../src/client/client.ts';
 import { closeAfter } from './teardown.ts';
 import { concatInfo } from '../src/protocol/udh.ts';
diff --git a/test/message-class.test.ts b/test/message-class.test.ts
index 9d0d4a5..6b3ed7c 100644
--- a/test/message-class.test.ts
+++ b/test/message-class.test.ts
@@ -2,14 +2,14 @@ import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
 import type { PduObjectInput } from '../src/codec/pdu.ts';
 import type { SendSmsDeps } from '../src/messages/submit.ts';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
 import type { TestContext } from 'node:test';
 import { bindToSmsc, dummySmsc } from './dummy-smsc.ts';
 import { client } from '../src/client/client.ts';
 import { closeAfter } from './teardown.ts';
 import { messageClassOf } from '../src/codec/encodings.ts';
-import { paramNumber } from '../src/codec/field-types.ts';
+import { paramNumber } from '../src/codec/types.ts';
 import { pduToObj } from '../src/codec/pdu.ts';
 import { server } from '../src/server/server.ts';
 import { silentLog } from '../src/log.ts';
diff --git a/test/messaging-mode.test.ts b/test/messaging-mode.test.ts
index 4b97e3f..fd0b1d7 100644
--- a/test/messaging-mode.test.ts
+++ b/test/messaging-mode.test.ts
@@ -2,12 +2,12 @@ import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
 import type { PduObjectInput } from '../src/codec/pdu.ts';
 import type { SendSmsDeps } from '../src/messages/submit.ts';
-import type { Session } from '../src/session.ts';
+import type { Session } from '../src/session/session.ts';
 import type { SubmitMessagingMode } from '../src/codec/constants.ts';
 import type { TestContext } from 'node:test';
 import { bindToSmsc, dummySmsc } from './dummy-smsc.ts';
 import { consts, submitMessagingModes } from '../src/codec/constants.ts';
-import { paramNumber } from '../src/codec/field-types.ts';
+import { paramNumber } from '../src/codec/types.ts';
 import { pduToObj } from '../src/codec/pdu.ts';
 import { silentLog } from '../src/log.ts';
 import { submitSms } from '../src/messages/submit.ts';
diff --git a/test/operator-receipts.test.ts b/test/operator-receipts.test.ts
index 03d3bb3..c02ae29 100644
--- a/test/operator-receipts.test.ts
+++ b/test/operator-receipts.test.ts
@@ -1,11 +1,11 @@
 import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
-import type { Dlr, Receipt } from '../src/protocol/receipt.ts';
-import type { MessageDlr } from '../src/session.ts';
+import type { Dlr, Receipt } from '../src/protocol/dlr.ts';
+import type { MessageDlr } from '../src/session/session.ts';
 import type { PduObject, TlvInputs } from '../src/codec/pdu.ts';
 import { bindToSmsc, dummySmsc } from './dummy-smsc.ts';
 import { consts } from '../src/codec/constants.ts';
-import { dlrFromPdu, parseReceipt, receiptCodes, transientStates } from '../src/protocol/receipt.ts';
+import { dlrFromPdu, parseReceipt, receiptCodes, transientStates } from '../src/protocol/dlr.ts';
 import { objToPdu, pduToObj } from '../src/codec/pdu.ts';
 
 /**
diff --git a/test/pdu-framer.test.ts b/test/pdu-framer.test.ts
index 3bafb85..fa4d538 100644
--- a/test/pdu-framer.test.ts
+++ b/test/pdu-framer.test.ts
@@ -1,6 +1,6 @@
 import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
-import { PduFramer } from '../src/codec/framer.ts';
+import { PduFramer } from '../src/codec/pdu-framer.ts';
 import { objToPdu } from '../src/codec/pdu.ts';
 
 function pdu(seqNr: number): Buffer {
diff --git a/test/pdu.test.ts b/test/pdu.test.ts
index c363efc..73179a2 100644
--- a/test/pdu.test.ts
+++ b/test/pdu.test.ts
@@ -2,7 +2,7 @@ import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
 import { PduRefusedError, refusalAnswer } from '../src/codec/refusal.ts';
 import { isCommand, isResp, objToPdu, pduReturn, pduToObj } from '../src/codec/pdu.ts';
-import { paramText } from '../src/codec/field-types.ts';
+import { paramText } from '../src/codec/types.ts';
 import { isTlvName, tlvsById } from '../src/codec/tlvs.ts';
 
 function encode(...args: Parameters<typeof objToPdu>): Buffer {
diff --git a/test/readme.test.ts b/test/readme.test.ts
index 1cb446b..5853bd9 100644
--- a/test/readme.test.ts
+++ b/test/readme.test.ts
@@ -1,8 +1,8 @@
 import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
-import type { Dlr } from '../src/protocol/receipt.ts';
-import type { Session } from '../src/session.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Dlr } from '../src/protocol/dlr.ts';
+import type { Session } from '../src/session/session.ts';
+import type { Sms } from '../src/session/sms.ts';
 import type { SmppLog } from '../src/log.ts';
 import type { SmppServer } from '../src/server/server.ts';
 import type { TestContext } from 'node:test';
diff --git a/test/session-extras.test.ts b/test/session-extras.test.ts
index e362ef2..530b373 100644
--- a/test/session-extras.test.ts
+++ b/test/session-extras.test.ts
@@ -2,28 +2,28 @@ import assert from 'node:assert/strict';
 import net from 'node:net';
 import test, { describe } from 'node:test';
 import type { Collected, LostGroup } from '../src/messages/reassembly.ts';
-import type { Dlr } from '../src/protocol/receipt.ts';
-import type { ErrorName } from '../src/codec/statuses.ts';
-import type { IncomingRequestsOptions } from '../src/session/requests-in.ts';
+import type { Dlr } from '../src/protocol/dlr.ts';
+import type { ErrorName } from '../src/codec/errors.ts';
+import type { IncomingRequestsOptions } from '../src/session/incoming-requests.ts';
 import type { HeldMessagesOptions, MessageHold } from '../src/session/held-messages.ts';
 import type { MessageState } from '../src/codec/constants.ts';
-import type { MessageDlr } from '../src/session.ts';
+import type { MessageDlr } from '../src/session/session.ts';
 import type { PduObject, PduObjectInput } from '../src/codec/pdu.ts';
 import type { Result } from '../src/result.ts';
 import type { SendSmsResult } from '../src/messages/submit.ts';
 import type { SmppLog } from '../src/log.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Sms } from '../src/session/sms.ts';
 import type { SmppServer } from '../src/server/server.ts';
 import type { TestContext } from 'node:test';
 import { HeldMessages } from '../src/session/held-messages.ts';
-import { IncomingRequests, refusedSegmentStatus } from '../src/session/requests-in.ts';
+import { IncomingRequests, refusedSegmentStatus } from '../src/session/incoming-requests.ts';
 import { UnansweredError } from '../src/unanswered-error.ts';
-import { createSms } from '../src/sms.ts';
-import { LinkLife } from '../src/link-life.ts';
+import { createSms } from '../src/session/sms.ts';
+import { LinkLife } from '../src/session/link-life.ts';
 import { SendWindow } from '../src/session/send-window.ts';
 import { Reassembler, decodeSegments } from '../src/messages/reassembly.ts';
-import { Session } from '../src/session.ts';
-import { DlrMerger } from '../src/messages/receipt-merge.ts';
+import { Session } from '../src/session/session.ts';
+import { DlrMerger } from '../src/messages/dlr-merger.ts';
 import { PduRefusedError } from '../src/codec/refusal.ts';
 import { objToPdu } from '../src/codec/pdu.ts';
 import { checkSessionOptions, defaults } from '../src/options.ts';
@@ -32,8 +32,8 @@ import { client } from '../src/client/client.ts';
 import { closeAfter, closeListenerAfter } from './teardown.ts';
 import { concatOf } from '../src/protocol/concat.ts';
 import { consts } from '../src/codec/constants.ts';
-import { errors } from '../src/codec/statuses.ts';
-import { paramNumber, paramText } from '../src/codec/field-types.ts';
+import { errors } from '../src/codec/errors.ts';
+import { paramNumber, paramText } from '../src/codec/types.ts';
 import { server } from '../src/server/server.ts';
 import { silentLog } from '../src/log.ts';
 import { splitMessage } from '../src/message.ts';
diff --git a/test/session.test.ts b/test/session.test.ts
index ee84322..30dccff 100644
--- a/test/session.test.ts
+++ b/test/session.test.ts
@@ -1,17 +1,17 @@
 import assert from 'node:assert/strict';
 import net from 'node:net';
 import test, { describe } from 'node:test';
-import type { Dlr } from '../src/protocol/receipt.ts';
+import type { Dlr } from '../src/protocol/dlr.ts';
 import type { PduObject, PduObjectInput } from '../src/codec/pdu.ts';
-import type { Sms } from '../src/sms.ts';
+import type { Sms } from '../src/session/sms.ts';
 import type { ServerOptions, SmppServer } from '../src/server/server.ts';
 import type { SmppLog } from '../src/log.ts';
 import type { TestContext } from 'node:test';
 import type { VoidResult } from '../src/result.ts';
-import { DlrMerger } from '../src/messages/receipt-merge.ts';
-import { PduFramer } from '../src/codec/framer.ts';
-import { ReconnectLoop } from '../src/reconnect-loop.ts';
-import { Session } from '../src/session.ts';
+import { DlrMerger } from '../src/messages/dlr-merger.ts';
+import { PduFramer } from '../src/codec/pdu-framer.ts';
+import { ReconnectLoop } from '../src/session/reconnect-loop.ts';
+import { Session } from '../src/session/session.ts';
 import { bindCommands } from '../src/protocol/bind.ts';
 import { checkSessionOptions } from '../src/options.ts';
 import { client } from '../src/client/client.ts';
@@ -19,7 +19,7 @@ import { closeAfter, closeListenerAfter } from './teardown.ts';
 import { consts } from '../src/codec/constants.ts';
 import { PduRefusedError } from '../src/codec/refusal.ts';
 import { isCommand, objToPdu, pduReturn, pduToObj } from '../src/codec/pdu.ts';
-import { paramText } from '../src/codec/field-types.ts';
+import { paramText } from '../src/codec/types.ts';
 import { server } from '../src/server/server.ts';
 import { bareTlvHeader, pduBytes, shortened, truncatedTlv, withUnknownCmdId } from './raw-pdus.ts';
 import { silentLog } from '../src/log.ts';
diff --git a/test/tls.test.ts b/test/tls.test.ts
index 056f93b..c65ea4b 100644
--- a/test/tls.test.ts
+++ b/test/tls.test.ts
@@ -1,7 +1,7 @@
 import assert from 'node:assert/strict';
 import net from 'node:net';
 import test, { describe } from 'node:test';
-import type { Sms } from '../src/sms.ts';
+import type { Sms } from '../src/session/sms.ts';
 import type { SmppServer } from '../src/server/server.ts';
 import type { TestContext } from 'node:test';
 import { Log } from '@larvit/log';
diff --git a/test/types.test.ts b/test/types.test.ts
index aec5399..b8c329a 100644
--- a/test/types.test.ts
+++ b/test/types.test.ts
@@ -1,7 +1,7 @@
 import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
-import type { DestAddress, UnsuccessSme } from '../src/codec/field-types.ts';
-import { paramText, types } from '../src/codec/field-types.ts';
+import type { DestAddress, UnsuccessSme } from '../src/codec/types.ts';
+import { paramText, types } from '../src/codec/types.ts';
 import { tlvs } from '../src/codec/tlvs.ts';
 
 describe('integers', () => {
diff --git a/test/unsendable.test.ts b/test/unsendable.test.ts
index d7cbb67..a9bacc2 100644
--- a/test/unsendable.test.ts
+++ b/test/unsendable.test.ts
@@ -6,7 +6,7 @@ import { bindToSmsc, dummySmsc } from './dummy-smsc.ts';
 import { decodeMessage } from '../src/message.ts';
 import { messageOctets } from '../src/protocol/message-body.ts';
 import { objToPdu, pduToObj } from '../src/codec/pdu.ts';
-import { paramNumber, paramText } from '../src/codec/field-types.ts';
+import { paramNumber, paramText } from '../src/codec/types.ts';
 import { silentLog } from '../src/log.ts';
 import { submitSms } from '../src/messages/submit.ts';
 
diff --git a/todo.md b/todo.md
index f73b491..58deb96 100644
--- a/todo.md
+++ b/todo.md
@@ -230,6 +230,8 @@ to the plan are [plan 3 §8](docs/comprehension-rewrite/plan-3.md#8-architecture
         reference counter goes to `SmppClient` in the lifecycle split.
       - The `gsm7` rename, A6 included: `'ASCII'` becomes `'GSM7'` in every export.
       - A test that fails on a spec citation without its sentence.
+      - Settle where `encodeBody()` and `decodeMessage()` land before splitting `message.ts`: `codec/pdu.ts`
+        reads them, so a home in `protocol/` is an upward edge.
 - [ ] **Build `messages/` on a `BoundedStore` that enforces its own bounds.** Reassembly refuses at its
       bound instead of evicting, recorded against goals 2 and 4; the receipt merge follows Q8 and its
       spent set expires by age. README's bound text is updated.
@@ -250,6 +252,17 @@ to the plan are [plan 3 §8](docs/comprehension-rewrite/plan-3.md#8-architecture
 
 ### Correctness
 
+- [ ] **Bound a rebind's wait when `responseTimeout` is 0.** `comeBackUp()` arms no timers until the
+      bind is answered, so an SMSC that takes the TCP connection and never answers leaves
+      `ReconnectLoop` attempting forever: no `close`, no next attempt. `answering()` already falls
+      back to the default for held messages; the bind has no such floor. From the 2026-09-30 scoring
+      run; confirm with a test first.
+
+- [ ] **Type a parsed `short_message` as what the parser puts there.** `parsePdu()` replaces it with
+      a decoded string wherever no UDH is present, while `PduParams<'submit_sm'>['short_message']`
+      is `Buffer` and `isCommand()`'s docstring calls the narrowing sound. Public type; from the
+      2026-09-30 scoring run.
+
 - [ ] **Refuse to open a link that dropped while its rebind was answered.** A peer sending
       `bind_resp` and FIN together can tear the link down before `comeBackUp()` resumes; it then
       calls `link.open()` on a `down` link, `resetTimers()` skips, and `attempt()` reports success,
@@ -336,7 +349,7 @@ to the plan are [plan 3 §8](docs/comprehension-rewrite/plan-3.md#8-architecture
 ### Shape — 6 today, and the gate is 7
 
 - [ ] **Answer "is this a bind command" in one place.** `bindCommands` (read by
-      `session/requests-in.ts`, `session/outgoing-requests.ts` and `test/session.test.ts`) and
+      `session/incoming-requests.ts`, `session/outgoing-requests.ts` and `test/session.test.ts`) and
       `bindTypeFromCommand()` (read by `server.ts` and `checkedBind()`) each list the three bind
       commands, so a fourth added to one is missed by the other. Derive the list from the function,
       or the reverse. From the stability review of #42.
@@ -442,7 +455,7 @@ to the plan are [plan 3 §8](docs/comprehension-rewrite/plan-3.md#8-architecture
 
 - [ ] **Narrow the `src/codec/` table lint exemption to the four table files.** Its stated reason — "the
       spec tables are data: their length tracks the specification, not any complexity" — is false for
-      `codec/field-types.ts`, which is 595 lines of wire codec with 25 functions and is the file that parses
+      `codec/types.ts`, which is 595 lines of wire codec with 25 functions and is the file that parses
       hostile input from the network. It carries more over-budget methods than any other file in the
       repo, under a suppression written for something else.
 
@@ -500,7 +513,7 @@ to the plan are [plan 3 §8](docs/comprehension-rewrite/plan-3.md#8-architecture
       `idleTimeout: '5000'` is refused with `got 5000` — a value the reader reads as correct — where
       `connectTimeout` quotes it. `namedValue()`'s four sites — `messagingMode`, `encoding`, the time
       options and `smsIdFormat` — are the same defect once more: there `true` and `'true'` both print
-      as `true`. One fix closes all three, and `valueText()` in `codec/field-types.ts` is the quoted
+      as `true`. One fix closes all three, and `valueText()` in `codec/types.ts` is the quoted
       spelling to take it from. Raised by review, 2026-09-20.
 
 - [ ] **Refuse a send the codec cannot build before it waits for a link and a window slot.** Today
@@ -537,7 +550,7 @@ to the plan are [plan 3 §8](docs/comprehension-rewrite/plan-3.md#8-architecture
       Maintainer's ask, 2026-09-14; not started until asked.
 
 - [ ] **Count what is left of a budget one way in `leftOf()` and `LinkLife`.** Today they are one
-      concept counted twice. `session/waiting.ts` reads what is left of a budget as `Math.max(1,
+      concept counted twice. `session/idle-waiters.ts` reads what is left of a budget as `Math.max(1,
       deadline - now)`, because 0 means "forever" there; `link-life.ts` runs the same subtraction
       and calls `<= 0` expired. Neither is reachable from the other, so nothing can disagree today,
       but a reader who learns one and applies it to the other is wrong. A budget type both take