diff --git a/CHANGELOG.md b/CHANGELOG.md
index a866efcd..82776267 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,101 @@
 
 All notable changes to kalshi-sdk will be documented in this file.
 
+## 2.6.0 — 2026-05-22
+
+Post-v2.5 independent reviewer audit closure (`#273` follow-on). 7 issues
+(`#295`–`#301`) identified by a fresh 7-agent parallel review of v2.5.0 across
+security, HTTP transport, WebSocket reliability, models/types, REST resources,
+performance, and docs/testing. Executed across 3 sequential waves (W0 docs,
+W1 money/correctness, W2 polish) in disjoint git worktrees. 7 PRs merged;
+main is mypy --strict clean, ruff clean, 2780+ unit tests passing.
+
+### Breaking changes
+
+Two behavioral fences; both surface bugs that were already wrong.
+
+- **`int` request fields reject `bool`** (`#295`). Per-field `StrictInt`
+  annotation on every money-routing / counting integer of every Request
+  model: `subaccount`, `exchange_index`, `expiration_ts`, `reduce_by`,
+  `reduce_to`, `contracts_limit`, `contracts`, `from_subaccount`,
+  `to_subaccount`, `amount_cents`, `subaccount_number` across V1 + V2.
+  `bool` is an `int` subclass, so a caller passing `True`/`False` used to
+  silently route to subaccount 1 / transfer 1 cent / decrease by 1 contract
+  with no error. Now raises `ValidationError` at construction. The existing
+  `buy_max_cost` validator (`#243`) is unchanged. New `kalshi.StrictInt`
+  alias is exported for downstream models.
+- **`KALSHI-ACCESS-*` in `extra_headers` is rejected** (`#298`). Both
+  `KalshiClient(..., config=KalshiConfig(extra_headers=...))` at
+  construction time and per-request `extra_headers=` kwargs now raise
+  `ValueError` if any key (case-insensitive) starts with `kalshi-access-`.
+  Previously a caller-supplied `'kalshi-access-key'` (lowercase) co-existed
+  with the SDK-signed `KALSHI-ACCESS-KEY` and httpx shipped both raw header
+  lines — a forge surface even though the documented contract promises
+  auth headers are SDK-managed.
+
+### Critical (money-risk fixes)
+
+- **`int` request fields reject `bool`** (`#295`, see Breaking).
+- **Auth-header forge surface closed** (`#298`, see Breaking). Companion fix:
+  `_post(json=...)` / `_put(json=...)` / `_delete_with_body(json=...)` and
+  their async mirrors now pin `Content-Type: application/json` explicitly,
+  preventing a caller-supplied `'content-type': 'text/plain'` in
+  `extra_headers` from causing httpx to ship a JSON body labelled as
+  plain text.
+- **WebSocket session re-entry is rejected** (`#297`). `KalshiWebSocket._start()`
+  used to silently rebuild every manager on nested or re-used `connect()`,
+  orphaning the outer session's subscriptions and recv task with no error.
+  Now raises `RuntimeError` with a clear message. `_stop()` clears the
+  manager refs after teardown so the same instance can be cleanly reused
+  for a fresh `connect()` once the prior session exits. A partial connect
+  failure (auth/network) also resets state cleanly via a `BaseException`
+  cleanup block, so a failed connect no longer permanently bricks the
+  instance.
+
+### High-impact correctness
+
+- **`KalshiConfig.extra_headers` validated at construction** (`#298`). Closes
+  the construction-time bypass that survived the per-request guard.
+- **Case-insensitive header merge** (`#298`). New `_ci_merge` ensures a
+  caller-supplied `'x-foo'` and SDK-set `'X-Foo'` collapse to one wire
+  entry rather than co-existing.
+- **Public `OrderbookManager.apply_snapshot()` keeps no-aliasing contract**
+  (`#296`). Snapshot/delta input messages remain safe to reuse after a
+  public `apply_snapshot()` call — the manager defensively copies the
+  adopted dicts. The recv loop continues to skip the copy via
+  `_apply_snapshot_inplace` for the hot-path perf win (#263).
+
+### Performance
+
+- **Orderbook snapshot adoption restored to identity** (`#296`). The
+  `dict(msg.msg.yes)` / `dict(msg.msg.no)` wrappers in
+  `_apply_snapshot_inplace` were silently nullifying the ~5x speedup
+  CHANGELOG #263 advertises. For a 200-level book that's 400 needless
+  re-hashes/reallocs per snapshot on the recv hot path. Wrappers dropped;
+  identity adoption restored on the bypass path.
+
+### Polish
+
+- **`Sync/AsyncTransport.close()` explicitly idempotent** (`#301`). New
+  `_closed` flag matches the `KalshiAuth` / `KalshiClient` pattern; second
+  and subsequent `close()` calls are no-ops. Documents the threading scope
+  honestly: sync is sequential-safe (worst case: one redundant
+  `httpx.Client.close()`, itself idempotent), async is fully race-free
+  under cooperative scheduling.
+- **`docs/resources/orders.md`**: removed stale `# ActionLiteral, defaults to
+  "buy"` inline comment that would have re-introduced the `#242` footgun
+  for readers (`#299`).
+- **`docs/configuration.md`**: reference table now lists `total_timeout`,
+  `ws_ping_interval`, `ws_close_timeout`, and `allow_unknown_host`; URL
+  validation prose updated for the v2.5 default-reject behavior (`#300`).
+
+### Additive
+
+- **`kalshi.StrictInt`** — new public type alias for downstream models that
+  want the same `bool`-rejection guard (`#295`).
+- **`kalshi/_constants.py`** (internal) — holds `AUTH_HEADER_PREFIX` to
+  eliminate drift between `_base_client.py` and `config.py` (`#298`).
+
 ## 2.5.0 — 2026-05-21
 
 Post-v2.4 multi-reviewer audit closure (`#273`). 34 issues across security,
diff --git a/ROADMAP.md b/ROADMAP.md
index 628ffef1..1db02d75 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -4,6 +4,20 @@
 
 See `CHANGELOG.md` for full release history.
 
+- **v2.6.0 (2026-05-22)** — post-v2.5 independent reviewer audit closure
+  (`#273` follow-on, 7 issues `#295`–`#301`). Two breaking changes folded
+  in: `int` request fields reject `bool` across V1+V2 via new
+  `kalshi.StrictInt` (`#295`); `KALSHI-ACCESS-*` in `extra_headers` is
+  rejected at both construction and per-request (`#298`). Critical fixes:
+  WS session re-entry guard with state reset on partial connect failure
+  (`#297`), case-insensitive transport header merge + explicit
+  `Content-Type` pin on JSON body helpers (`#298`). Performance: orderbook
+  snapshot identity adoption restored on the recv-loop bypass (`#296`),
+  with public `apply_snapshot` keeping its defensive copy. Polish:
+  `Sync/AsyncTransport.close()` idempotent (`#301`), docs corrections
+  (`#299`, `#300`). Executed across 3 sequential waves (W0 docs, W1
+  money/correctness, W2 polish) — 7 PRs merged.
+
 - **v2.5.0 (2026-05-21)** — post-v2.4 multi-reviewer SDK audit closure
   (#273, 34 issues across 7 surfaces). Critical fixes: WS seq watermark
   rolls back on validation failure (#241), REST/WS split-environment
diff --git a/docs/migration.md b/docs/migration.md
index 7a1f378c..5856fb43 100644
--- a/docs/migration.md
+++ b/docs/migration.md
@@ -1,5 +1,104 @@
 # Migration
 
+## v2.5 → v2.6
+
+v2.6 ships two behavioral fences, both surface bugs that were already wrong:
+``bool`` no longer slips through on integer request fields (`#295`), and
+``extra_headers`` cannot carry ``KALSHI-ACCESS-*`` keys (`#298`). Wire
+format is unchanged.
+
+### Breaking: `int` request fields reject `bool`
+
+Per `#295`, every integer field on every Request model that lacks a
+dedicated validator now rejects ``bool`` at construction. ``bool`` is an
+``int`` subclass, so a caller passing ``True``/``False`` silently became
+``1``/``0`` and money-routing fields (``subaccount``, ``from_subaccount``,
+``amount_cents``, ``count``, etc.) silently misrouted. The fix mirrors
+``CreateOrderRequest.buy_max_cost`` (`#243`) across all request models on
+both V1 and V2 surfaces:
+
+```python
+# v2.5 (silent True → 1)
+ApplySubaccountTransferRequest(
+    client_transfer_id=uuid4(),
+    from_subaccount=True,   # → 1, transfer from subaccount 1
+    to_subaccount=True,     # → 1, transfer TO subaccount 1
+    amount_cents=True,      # → 1, one cent
+)
+
+# v2.6 (raises ValidationError on each bool)
+ApplySubaccountTransferRequest(
+    client_transfer_id=uuid4(),
+    from_subaccount=True,   # ➜ ValidationError: bool is not a valid int here
+)
+```
+
+A new public alias ``kalshi.StrictInt = Annotated[int, BeforeValidator(...)]``
+is exported for downstream models that want the same guard.
+
+### Breaking: `KALSHI-ACCESS-*` rejected in `extra_headers`
+
+Per `#298`, the SDK promised in docs that auth headers could not be forged
+via ``extra_headers``. That promise relied on a case-sensitive Python dict
+merge: a caller-supplied lowercase ``"kalshi-access-key"`` co-existed with
+the SDK-signed uppercase ``"KALSHI-ACCESS-KEY"`` and httpx shipped both raw
+header lines on the wire — a forge surface even though the documented
+contract said otherwise. Now both the per-request ``extra_headers`` kwarg
+and ``KalshiConfig(extra_headers=...)`` reject any key (case-insensitive)
+that starts with ``kalshi-access-`` at the construction boundary:
+
+```python
+# v2.5 (silently shipped two KALSHI-ACCESS-KEY header lines)
+client.markets.list(
+    extra_headers={"kalshi-access-key": "forged"},
+)
+
+# v2.6 (raises ValueError naming the leaked keys)
+client.markets.list(
+    extra_headers={"kalshi-access-key": "forged"},
+)
+# ValueError: extra_headers must not include KALSHI-ACCESS-* keys ...
+
+# Same rejection now fires at construction:
+KalshiConfig(extra_headers={"kalshi-access-key": "x"})
+# ValueError
+```
+
+Companion behavior: `_post(json=...)` / `_put(json=...)` /
+`_delete_with_body(json=...)` (and async mirrors) now pin
+``Content-Type: application/json`` explicitly. A caller-supplied
+``extra_headers={"content-type": "text/plain"}`` previously suppressed
+httpx's implicit inference and shipped a JSON body labelled as plain
+text; the explicit pin prevents that. Most callers are unaffected.
+
+### Behavioral note: raw `subscribe_orderbook_delta` consumers
+
+Per `#296`, `OrderbookManager._apply_snapshot_inplace` now adopts
+``msg.msg.yes`` / ``.no`` by identity for the recv-loop hot path. Raw
+consumers of ``subscribe_orderbook_delta`` who receive an
+``OrderbookSnapshotMessage`` and hold a reference to ``msg.msg.yes`` /
+``.no`` will observe future delta mutations through that reference:
+
+```python
+# v2.6 raw subscriber
+async for msg in stream:
+    if isinstance(msg, OrderbookSnapshotMessage):
+        held = msg.msg.yes        # ← LIVE dict, mutated by next delta
+```
+
+The high-level ``client.orderbook(ticker)`` / ``subscribe_book(ticker)``
+iterators are unaffected — both materialize fresh ``Orderbook`` instances
+that are safe to retain. The public ``OrderbookManager.apply_snapshot()``
+is also unaffected: it defensively copies after the inplace adoption so
+the caller-supplied ``msg`` keeps its original dicts. If you need an
+immutable snapshot view from the raw stream, copy explicitly:
+
+```python
+async for msg in stream:
+    if isinstance(msg, OrderbookSnapshotMessage):
+        immutable_yes = dict(msg.msg.yes)
+```
+
 ## v2.4 → v2.5
 
 v2.5 ships two user-visible breaking changes — both surface bugs that
diff --git a/kalshi/__init__.py b/kalshi/__init__.py
index af3bf7cf..3822cea1 100644
--- a/kalshi/__init__.py
+++ b/kalshi/__init__.py
@@ -337,4 +337,4 @@
     "Withdrawal",
 ]
 
-__version__ = "2.5.0"
+__version__ = "2.6.0"
diff --git a/pyproject.toml b/pyproject.toml
index ab12c29b..24bf3e4a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "kalshi-sdk"
-version = "2.5.0"
+version = "2.6.0"
 description = "A professional Python SDK for the Kalshi prediction markets API"
 readme = "README.md"
 license = { text = "MIT" }