[BUG] Conversation history invalidated on subsequent turns

[jmarianski]

Preflight Checklist

• I have searched existing issues and this hasn't been reported yet
• This is a single bug report (please file separate reports for different bugs)
• I am using the latest version of Claude Code

What's Wrong?

While investigating huge token usage I've noticed it come due to fact suddenly my conversation history gets invalidated and all subsequent turns revert to only caching system prompt and huge cache writes.

What Should Happen?

Cache shouldn't drop due to history changes. History should not be updated. Or we shouldn't be charged for historical updates.

Error Messages/Logs

Analysis of token usage from the start of my analysis:

time        cache_read  cache_cr    input    out    model               stop        
----------  ----------  ----------  -------  -----  ------------------  ------------
22:22:48    312377      1944        1        215    opus-4-6            end_turn    
22:23:39    314321      493         3        159    opus-4-6            end_turn    
22:24:19    314814      172         3        108    opus-4-6            end_turn    
22:33:42    0           0           8        1      haiku-4-5-20251001  max_tokens  <-- resume
22:34:26    11428       305735      3        213    opus-4-6            tool_use    <-- irrelevant cache rewrite after restart
22:34:35    317163      579         1        239    opus-4-6            tool_use    
22:34:43    317742      566         1        152    opus-4-6            end_turn    
22:37:13    318308      245         3        96     opus-4-6            end_turn    
07:55:55    0           0           8        1      haiku-4-5-20251001  max_tokens  <-- resume
07:56:22    11428       163547      3        143    opus-4-6            tool_use    <-- partial cache regenerate (wth?)
07:56:40    174975      358         1        90     opus-4-6            end_turn    
07:57:25    11428       307626      3        87     opus-4-6            end_turn    <-- full cache regenerate
07:57:51    319054      108         3        89     opus-4-6            tool_use    
07:58:05    319162      712         1        448    opus-4-6            tool_use    
07:58:21    319874      833         1        367    opus-4-6            end_turn    
07:59:21    320707      393         3        414    opus-4-6            tool_use    
07:59:34    321100      609         1        560    opus-4-6            tool_use    
07:59:47    321709      948         1        512    opus-4-6            tool_use    
08:00:10    322657      615         1        348    opus-4-6            end_turn    
08:03:00    323272      426         3        530    opus-4-6            tool_use    
08:03:12    323698      972         1        468    opus-4-6            tool_use    
08:03:22    324670      529         1        167    opus-4-6            end_turn    
08:03:29    325199      215         3        28     opus-4-6            end_turn    
08:05:30    0           0           8        1      haiku-4-5-20251001  max_tokens  <-- resume
08:05:48    11428       187695      3        155    opus-4-6            tool_use    
08:06:06    199123      876         1        780    opus-4-6            tool_use    
08:06:25    199999      2199        1        1285   opus-4-6            tool_use    
08:06:38    202198      1633        1        302    opus-4-6            end_turn    
08:08:06    203831      481         3        88     opus-4-6            tool_use    
08:08:17    204312      408         1        175    opus-4-6            end_turn    
08:09:16    204720      206         3        154    opus-4-6            end_turn    
08:10:25    204926      228         3        503    opus-4-6            tool_use    
08:10:34    205154      1193        1        507    opus-4-6            tool_use    
08:10:45    206347      1007        1        247    opus-4-6            end_turn    
08:10:54    0           0           8        1      haiku-4-5-20251001  max_tokens  <-- resume
08:11:16    11428       195983      3        136    opus-4-6            tool_use    
08:11:37    207411      616         1        1207   opus-4-6            tool_use    
08:11:49    208027      1457        1        290    opus-4-6            end_turn    
08:12:02    209484      323         3        270    opus-4-6            end_turn    
08:12:27    209807      284         3        190    opus-4-6            tool_use    
08:12:39    210091      314         1        278    opus-4-6            tool_use    
08:13:01    210405      728         1        1219   opus-4-6            tool_use    
08:13:18    211133      1465        1        449    opus-4-6            end_turn    
08:15:28    212598      599         3        325    opus-4-6            end_turn    
08:16:26    213197      334         3        209    opus-4-6            end_turn    
08:18:00    213531      288         3        137    opus-4-6            tool_use    
08:18:07    213819      1131        1        122    opus-4-6            tool_use    
08:18:15    214950      140         1        193    opus-4-6            tool_use    
08:18:29    215090      1114        1        269    opus-4-6            tool_use    
08:18:54    216204      10504       1        336    opus-4-6            tool_use    <-- cache starts breaking down due to history change*
08:19:07    216204      11815       1        228    opus-4-6            tool_use    
08:19:17    216204      12990       1        134    opus-4-6            tool_use    
08:19:38    216204      13341       1        301    opus-4-6            tool_use    
08:20:04    216204      13758       1        426    opus-4-6            tool_use    
08:20:18    216204      15278       1        154    opus-4-6            tool_use    
08:20:46    216204      15778       1        508    opus-4-6            tool_use    
08:22:25    216204      17092       1        208    opus-4-6            tool_use    
08:22:51    216204      17894       1        660    opus-4-6            tool_use    
08:23:22    11428       224502      1        315    opus-4-6            end_turn    <-- cache cannot get regenerated, reverting to full cache write
08:24:47    11428       224953      3        871    opus-4-6            tool_use    
08:25:10    11428       227259      1        597    opus-4-6            tool_use    
08:25:24    11428       228249      1        356    opus-4-6            tool_use    
08:25:43    11428       228669      1        825    opus-4-6            tool_use    
08:26:01    11428       229763      1        468    opus-4-6            tool_use    
08:26:22    11428       230278      1        339    opus-4-6            end_turn    
08:28:07    11428       230642      3        442    opus-4-6            end_turn    
08:37:30    11428       231432      3        430    opus-4-6            end_turn    

---
(Ignore hour, it's another day)
When running "npx @anthropic-ai/claude-code"
21:28:59    11374       46622       1        473    opus-4-6            tool_use    <-- still on standalone binary
22:02:13    0           0           8        1      haiku-4-5-20251001  max_tokens  <-- I tried resuming a couple of times
22:02:23    0           0           340      11     haiku-4-5-20251001  end_turn    
22:02:25    11374       15278       3        21     opus-4-6            end_turn    
22:04:51    0           0           8        1      haiku-4-5-20251001  max_tokens  
22:04:58    0           0           341      11     haiku-4-5-20251001  end_turn    
22:05:00    11374       15194       3        20     opus-4-6            end_turn    
22:09:20    0           0           8        1      haiku-4-5-20251001  max_tokens  
22:09:35    0           0           8        1      haiku-4-5-20251001  max_tokens  
22:12:16    0           0           341      11     haiku-4-5-20251001  end_turn    
22:12:18    11374       15194       3        21     opus-4-6            end_turn    
22:15:36    0           0           8        1      haiku-4-5-20251001  max_tokens  
23:22:46    0           0           8        1      haiku-4-5-20251001  max_tokens  
23:23:06    0           0           341      12     haiku-4-5-20251001  end_turn    
23:23:09    11374       17262       3        19     opus-4-6            end_turn    
23:23:26    28636       27          3        12     opus-4-6            end_turn    
23:31:41    0           0           8        1      haiku-4-5-20251001  max_tokens  
23:31:50    0           0           345      13     haiku-4-5-20251001  end_turn    
23:31:54    11374       17188       3        32     opus-4-6            end_turn      <-- start of npx trials
23:32:25    28562       51          3        167    opus-4-6            end_turn    
23:33:52    28613       320         3        666    opus-4-6            end_turn    
23:34:55    0           0           8        1      haiku-4-5-20251001  max_tokens  
23:35:12    0           0           355      15     haiku-4-5-20251001  end_turn  
23:35:22    11374       17198       3        328    opus-4-6            end_turn    
23:36:50    28572       367         3        500    opus-4-6            end_turn    
23:37:15    28939       506         3        143    opus-4-6            tool_use    
23:37:19    29445       523         1        91     opus-4-6            tool_use    
23:37:56    29968       4869        1        1284   opus-4-6            tool_use    
23:38:06    34837       1343        1        173    opus-4-6            end_turn    
23:38:19    36180       219         3        151    opus-4-6            tool_use    
23:38:27    36399       9511        1        341    opus-4-6            tool_use    
23:38:33    45910       442         73       77     opus-4-6            tool_use    
23:38:37    46352       250         1        77     opus-4-6            tool_use    
23:38:42    46602       1161        1        134    opus-4-6            tool_use    
23:38:59    47763       415         1        369    opus-4-6            tool_use    
23:39:06    48178       427         1        96     opus-4-6            tool_use    
23:39:09    48605       393         1        77     opus-4-6            tool_use    
23:39:13    48605       639         1        152    opus-4-6            tool_use    
23:40:17    11374       38207       3        362    opus-4-6            end_turn    
23:41:35    49581       438         3        766    opus-4-6            end_turn    
23:43:02    0           0           8        1      haiku-4-5-20251001  max_tokens  <-- another session
23:43:23    11374       40201       3        97     opus-4-6            tool_use    
23:43:30    51575       122         1        310    opus-4-6            tool_use    
23:43:35    51697       408         1        152    opus-4-6            tool_use    
23:43:41    52105       219         93       170    opus-4-6            tool_use    
23:43:49    52324       442         1        259    opus-4-6            tool_use    
23:43:54    52766       558         1        102    opus-4-6            tool_use    
23:44:08    53324       2593        1        403    opus-4-6            end_turn    
23:51:33    0           0           8        1      haiku-4-5-20251001  max_tokens  
23:52:30    55917       431         3        187    opus-4-6            tool_use    
23:54:20    56348       292         37       284    opus-4-6            tool_use    
23:54:29    56640       612         158      492    opus-4-6            tool_use    
23:54:54    60657       13          3        508    opus-4-6            end_turn    
23:58:58    60670       717         2        454    opus-4-6            tool_use    
23:59:05    61387       847         1        336    opus-4-6            tool_use    
23:59:23    62234       1282        1        674    opus-4-6            tool_use    
23:59:34    63516       1024        1        506    opus-4-6            tool_use    
23:59:45    64540       583         1        264    opus-4-6            tool_use    
23:59:53    65123       284         1        393    opus-4-6            tool_use    
00:00:10    65407       470         1        887    opus-4-6            tool_use    
00:03:07    65877       1024        1        871    opus-4-6            tool_use    
00:03:16    66901       2098        1        538    opus-4-6            tool_use    
00:03:25    68999       1492        1        379    opus-4-6            tool_use    
00:03:36    70491       1043        1        640    opus-4-6            tool_use    
00:03:43    71534       704         1        233    opus-4-6            tool_use    
00:03:51    72238       250         1        148    opus-4-6            tool_use    
00:03:58    72488       355         1        249    opus-4-6            tool_use    
00:04:03    72843       396         1        259    opus-4-6            tool_use    
00:04:10    73239       435         1        278    opus-4-6            tool_use    
00:04:31    73674       359         1        941    opus-4-6            tool_use    
00:04:45    74033       1595        1        662    opus-4-6            tool_use    
00:05:00    75628       914         1        830    opus-4-6            tool_use    
00:05:18    76542       1610        1        963    opus-4-6            tool_use    
00:05:31    78152       1379        1        640    opus-4-6            tool_use    
00:05:41    79531       1374        1        549    opus-4-6            tool_use    
00:05:51    80905       1576        1        550    opus-4-6            tool_use    
00:06:06    82481       629         1        986    opus-4-6            tool_use    
00:06:20    83110       1102        1        994    opus-4-6            tool_use    
00:06:30    84212       1074        1        578    opus-4-6            tool_use    
00:06:48    85286       2418        1        854    opus-4-6            tool_use    
00:07:01    87704       880         1        555    opus-4-6            tool_use    
00:07:13    88584       818         1        601    opus-4-6            tool_use    
00:07:30    89402       2165        1        520    opus-4-6            end_turn    
00:11:02    91567       542         3        691    opus-4-6            tool_use    
00:11:12    92109       777         1        733    opus-4-6            tool_use    
00:11:25    92886       1042        1        578    opus-4-6            tool_use    
00:11:39    93928       3347        1        694    opus-4-6            tool_use    
00:12:21    98211       39          3        442    opus-4-6            end_turn    
00:13:24    98250       462         3        161    opus-4-6            tool_use    
00:13:32    98712       274         1        178    opus-4-6            end_turn    
00:15:06    98986       190         3        237    opus-4-6            tool_use    
00:15:37    99176       362         1        1202   opus-4-6            tool_use    
00:15:42    6637        16169       2        114    opus-4-6            tool_use    
00:15:44    99538       1427        1        280    opus-4-6            tool_use    
00:15:47    22806       3503        1        160    opus-4-6            tool_use    
00:15:49    100965      2929        1        52     opus-4-6            end_turn    <-- my joy is great at this point
00:15:50    26309       191         1        91     opus-4-6            tool_use    
00:15:54    26500       217         1        92     opus-4-6            tool_use    
00:15:57    26717       152         1        88     opus-4-6            tool_use    
00:16:02    26869       607         3        125    opus-4-6            tool_use    
00:16:06    27476       146         1        166    opus-4-6            tool_use    
00:16:09    27622       430         1        105    opus-4-6            tool_use    
00:16:14    28052       123         1        109    opus-4-6            tool_use    
00:16:19    28052       542         1        176    opus-4-6            tool_use    
00:16:23    28594       440         1        95     opus-4-6            tool_use    
00:16:28    29034       120         1        112    opus-4-6            tool_use    
00:16:32    29154       139         1        180    opus-4-6            tool_use    
00:16:37    29293       256         1        206    opus-4-6            tool_use    
00:17:09    29549       1065        1        82     opus-4-6            tool_use    
00:17:12    30614       131         1        117    opus-4-6            tool_use    
00:17:24    30745       135         1        79     opus-4-6            tool_use    
00:17:28    30745       237         1        100    opus-4-6            tool_use    
00:17:35    30982       140         1        138    opus-4-6            tool_use    
00:17:39    31122       222         1        112    opus-4-6            tool_use    
00:17:46    31344       226         1        257    opus-4-6            tool_use    
00:17:51    31570       288         1        125    opus-4-6            tool_use    
00:17:56    31858       214         1        128    opus-4-6            tool_use    
00:18:01    32072       316         1        139    opus-4-6            tool_use    
00:18:04    32388       487         1        116    opus-4-6            tool_use    
00:18:09    32875       134         1        125    opus-4-6            tool_use    
00:19:29    33009       143         1        5925   opus-4-6            tool_use    
00:19:35    33152       5912        1        113    opus-4-6            tool_use    <-- yup, was at 100% usage at this point
00:19:36    0           0           0        0      -                   -           
00:19:36    0           0           0        0      -                   -           
10:08:54    11374       58355       3        270    opus-4-6            tool_use    <-- costly resume, but cache TTL = 1h in claude code
10:09:00    69729       538         1        277    opus-4-6            tool_use    
10:09:07    70267       7086        180      188    opus-4-6            tool_use    
10:09:14    77353       436         1        201    opus-4-6            tool_use    
10:09:18    77789       219         1        118    opus-4-6            tool_use    
10:09:34    78008       518         1        183    opus-4-6            tool_use    
10:10:40    78526       444         1        95     opus-4-6            tool_use    
10:10:46    78970       1213        1        185    opus-4-6            tool_use    
10:10:55    80183       996         1        270    opus-4-6            tool_use    
10:13:03    81179       602         1        268    opus-4-6            tool_use    
10:18:08    81781       675         1        121    opus-4-6            tool_use    
10:18:14    82456       148         1        226    opus-4-6            tool_use    
10:29:13    82604       823         1        184    opus-4-6            tool_use    
10:29:19    83427       889         1        239    opus-4-6            tool_use    
----------  ----------  ----------  -------  -----  ------------------  ------------


If you provide me with means, I can send you full request/response dumps

*- no idea if this cache breaking was due to me inspecting binary or some historical tool change happened on the background level.

Steps to Reproduce

Write "cch=00000" in command line and ask claude what does he see. He still should see "cch=00000". And token usage should be all "cache read" mostly, not "cache write" for subsequent requests.

Step to temporarily fix: npx @anthropic-ai/claude-code@2.1.34 // you need to fix it on older version to benefit from it

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Based on reports: 2.1.67

Claude Code Version

2.1.86 (Claude Code)

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

Similar issue: #34629 - this one relates to immediate start of conversation

Tool I wrote for debugging: https://gitlab.com/treetank/cc-diag

Verification script: https://gitlab.com/treetank/cc-diag/-/raw/c126a7890f2ee12f76d91bfb1cc92612ae95284e/test_cache.py

[github-actions]

Found 3 possible duplicate issues:

1. [BUG] Prompt cache regression in --print --resume since v2.1.69(?): cache_read never grows, ~20x cost increase #34629
2. [BUG] Prompt Cache Invalidation on Session Resume: Tool-Use Content Not Cached, Plugin State Changes Cause Full User Content Rewrite #27048
3. [BUG] Session resume loads zero conversation history — silently drops all context #40319

This issue will be automatically closed as a duplicate in 3 days.

• If your issue is a duplicate, please close it and 👍 the existing issue instead
• To prevent auto-closure, add a comment or 👎 this comment

🤖 Generated with Claude Code

[jmarianski]

This is not a duplicate. It doesn't relate to session resume, but a subsequent turn invalidation.

[RebelSyntax]

im collecting the same evidence. something breaks the cache and it never recovers. model switches mid session is an easy one to pinpoint. the billing header seems to be a proxy for whatever it is. possibly the dynamic tool loading or some sort of memory call back? not sure but the only way to recover seems to be starting a completely brand new session. otherwise cache writes grow unbounded and quickly devour premium tokens.

[jmarianski]

"model switches mid session" is one of the behaviors for saving compute done by anthropic, as stated in the email from the robot: "The 20% threshold you're seeing is actually by design for Max 5x plans. Claude Code automatically switches from Opus 4 to Sonnet 4 when you reach 20% of your rate limit (Max 20x users get 50%). This threshold is intentionally set to help preserve a good experience and prevent users from hitting their full rate limits too quickly."

I've had my findings now and it is I've expected: binary holds some code that is revealed after decompiling. Apparently they've secretly injected cch=hash (Zig Wyhash) into the body of a request if a header "anthropic-version" appears in the request. However, if at some point "cch=00000" appears in the body of a request, it will be infected. Reason? No clue. I'm trying to find it out.

It seems like a small side effect of some obscure tool use or some micro compaction that might have already been fixed. I mean I was trying to find out, however code doesn't allow currently for "cch=00000" to accidentally leak.

[jmarianski]

Full reverse engineering analysis of the sentinel replacement mechanism

Summary

Through MITM proxy capture + Ghidra reverse engineering of the Claude Code standalone binary (228MB ELF), I've identified the exact mechanism causing conversation history invalidation. The root cause is a native-layer sentinel replacement in Anthropic's custom Bun fork that rewrites the billing attribution header value on every API request.

The Mechanism

Located at VA 0x0374d610 in the standalone binary (v2.1.87) — inside the Zig HTTP header builder function (src/http.zig in Bun's source tree). This is the same function that builds Content-Length, User-Agent, Host, Accept-Encoding, etc.

Trigger condition: The replacement fires when ALL of these are true:

1. Request contains anthropic-version HTTP header (Wyhash = 0x58e54d60e1462681, verified via Bun.hash())
2. Request URL path contains /v1/messages
3. Request body contains the sentinel string cch=00000 (9 bytes)

What it does:

1. Searches the serialized JSON request body for the first occurrence of cch=00000
2. Hashes the entire request body (using a hash function with fixed seeds: 0xcf3c9b5975c738f4, 0x310521a7efdb6e6d, 0x6e52736ac806831e, 0xd01af9b9421ab897)
3. Converts 5 nibbles of the hash to hex characters using SIMD instructions (pshufb/pblendvb)
4. Writes the 5 hex characters in-place into the body buffer, replacing 00000

Decompiled pseudocode (reconstructed from Ghidra):

// Inside HTTP header builder — after iterating request headers
if (has_anthropic_version_header) {
    // Check URL contains "/v1/messages"
    // Built on stack as u64 LE immediates:
    local_c0 = 0x7373656d2f31762f;  // "/v1/mess"
    local_b8 = 0x73656761;          // "ages"
    if (memmem(url_ptr, url_len, &local_c0, 12) != NULL) {

        // Search body for sentinel "cch=00000"
        // Also built on stack:
        local_c0 = 0x303030303d686363;  // "cch=0000" LE
        local_b8 = 0x30;               // "0"
        offset = memmem(body_ptr, body_len, &local_c0, 9);

        if (offset != NULL) {
            // Hash the entire body
            hash_state = init(seeds...);
            hash_update(hash_state, body_ptr, body_len);
            hash_value = hash_finalize(hash_state);

            // Convert 5 nibbles to hex (SIMD)
            hex_chars = simd_nibble_to_hex(hash_value);

            // Write in-place: body[offset+4..offset+9] = hex chars
            *(uint32_t*)(body_ptr + 4 + offset) = hex_chars[0..3];
            *(char*)(body_ptr + 8 + offset) = hex_char_5th;
        }
    }
}

Key findings

1. Only the standalone binary does this — not the JS code

Confirmed experimentally:

Runtime	Replacement active?
Official standalone binary (228MB ELF)	YES
bun build --compile --bytecode cli.js (homebrew standalone)	NO
bun cli.js (standard Bun runtime)	NO
npx @anthropic-ai/claude-code (npm package)	NO

Same JavaScript code, same bytecode, same Bun standalone format — different behavior. The replacement is in Anthropic's custom Bun fork, compiled into the native Zig HTTP client.

2. Sentinel is hardcoded as stack immediates — invisible to string search

The pattern cch=00000 is built on the stack using MOV imm64 instructions:

MOV [rsp+X], 0x303030303d686363   ; "cch=0000" in little-endian
MOV byte [rsp+X+8], 0x30          ; "0" — completing "cch=00000"

This is why searching the binary for 63 63 68 3d (cch=) or 0x303030303d686363 as raw bytes in .text yields zero results — the bytes are part of instruction immediates, not contiguous string data.

3. Replacement value is a body hash, not random

The replacement value is deterministic per request body — it's a hash of the entire body with fixed seeds. But since the body changes every request (new messages, timestamps), the hash value changes too, making it appear random.

4. Only the FIRST occurrence is replaced

There is no loop — memmem finds the first match, replacement writes 5 bytes, and the function continues to build Content-Length headers. This means:

• If messages[] (which comes BEFORE system[] in the JSON body) contains cch=00000, that gets replaced instead of the billing header in system[0]
• The sentinel in system[0] survives — visible to the model as literal cch=00000

5. Header hashes identified

The function uses Zig's std.hash.Wyhash (seed=0, confirmed via Bun.hash()) for case-insensitive header name comparison:

Hash	Header
0x58e54d60e1462681	anthropic-version — triggers replacement
0xba5173bf47c57684	connection
0x4cc2547449bddafc	upgrade
0xfc8491525da4c9e3	content-length
0x308b6fc4af845531	transfer-encoding
0x2e6b2eda627d6669	user-agent
0x62b7d00b4bd17658	accept-encoding
0xfbb5acdf8484b6ef	accept
0x80bd44e8947f37d2	host
0x3dfa2d55bad7bb18	if-modified-since

6. Sentinel history

CC Version	cch=00000 in billing header?
1.0.0 – 2.0.0	No billing header at all
2.1.0 – 2.1.34	Billing header exists, but no cch field
2.1.36	cch=00000 introduced
2.1.36 – 2.1.87	Present in all versions

How this causes cache invalidation

The billing header cch=00000 is placed in system[0] by the JS function DG$(). On the standalone binary, the native replacement changes 00000 to a body-hash value (e.g., a3f1b) before the request leaves the process.

In normal sessions (no sentinel in conversation content): Only system[0] is affected. Since system[0] has cache_control: null (no caching), this doesn't break the cache prefix — system[2] (main prompt with cache_control: ephemeral) and messages[] remain stable.

When conversation content contains cch=00000: This happens when:

• CLAUDE.md discusses the billing mechanism (our research notes)
• Read/Grep tool reads the JS bundle or binary containing the sentinel
• User types the sentinel literally

Since messages[] comes BEFORE system[] in the JSON body, the sentinel in messages is replaced FIRST. The actual billing header in system[0] keeps 00000. But the changed value in messages breaks the cache prefix from that point onward.

Methodology

1. MITM proxy (mitm-addon.py via mitmproxy) capturing all API request/response payloads
2. Binary comparison: official standalone (228MB) vs homebrew bun build --compile (224MB) — same JS, different behavior
3. Ghidra 12.0.4 reverse engineering of the standalone ELF, identifying FUN_0374d610 as the HTTP header builder with injected replacement logic
4. radare2 disassembly for cross-referencing and function analysis
5. Bun.hash() to verify all header name hashes (Zig Wyhash, seed=0)
6. npm package analysis across versions 1.0.0 through 2.1.87, identifying cch=00000 introduction in v2.1.36
7. Controlled experiments: fresh session → resume → consecutive resumes with full payload diffing
8. 62 non-research project transcripts verified: zero accidental billing header leaks into messages

Related

This finding also explains the root cause of #34629 (cache regression on --print --resume since v2.1.69), where the deferred_tools_delta attachment introduced in v2.1.69 causes messages[0] to differ between fresh sessions and resumed sessions, independently breaking cache prefix matching.

[PHPCraftdream]

Great work!

[j0KZ]

i have spikes of about 200-300k tokens when this happens. this is why my cuota is being devoured